CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 62/574,017, filed October 18, 2017 by Shan Liu, and titled "Motion Vector Prediction and Merge Candidate Selection with Various Vector Precisions," which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present disclosure is generally related to video coding, and is specifically related to generation of motion vector candidate lists for coding video blocks via inter- prediction in video coding.

BACKGROUND

[0003] The amount of video data needed to depict even a relatively short video can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated across modern day telecommunications networks. The size of a video could also be an issue when the video is stored on a storage device because memory resources may be limited. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission or storage, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve compression ratio with little to no sacrifice in image quality are desirable.

SUMMARY

[0004] In an embodiment, the disclosure includes a method implemented in a video decoder. The method comprises receiving, at a receiver in the video decoder, a candidate list index in a bitstream; selecting, by a processor in the video decoder, a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block; applying, by the processor, the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block; determining, by the processor, a motion vector for the current block based on the candidate list of motion vectors and the candidate list index; and reconstructing, by the processor, the current block for display based on the motion vector. This approach selects from a group of patterns for generating a candidate list for inter-prediction instead of using a single pattern in all cases. This results in better compression when video blocks are encoded in an order other than raster order. Specifically, this approach determines the position of available (e.g., valid) coded blocks around the current block, and selects the pattern for candidate list generation based on such determination. This results in selecting patterns that have a high likelihood of including useful data to support block coding, and hence an increased likelihood of including a candidate vector that accurately describes motion of the current block.

[0005] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the candidate list is a merge candidate list or an adaptive motion vector prediction (AMVP) candidate list.

[0006] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a top right corner, and a top left corner of the current block when the available coded blocks are positioned above the current block and left of the current block. This approach selects candidate motion vectors from the top and left of the current block when the available coded blocks are to the top and left of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0007] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and right of the current block. This approach selects candidate motion vectors from the top and right of the current block when the available coded blocks are to the top and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0008] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and below the current block. This approach selects candidate motion vectors from the top and bottom of the current block when the available coded blocks are to the top and bottom of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0009] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from above, left, and right of the current block when the available coded blocks are above, left, and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0010] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, below the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from all around the current block when the available coded blocks are all around the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0011] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; then checking blocks in a B position with a common reference index with the current block; and then checking blocks in a B position with a scaled reference index.

[0012] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; then checking blocks in an A position with a common reference index with the current block; and then checking blocks in an A position with a scaled reference index. [0013] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index.

[0014] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0015] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index.

[0016] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0017] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the bitstream includes a maximum candidate list number, and wherein the selected candidate list determination pattern adds motion vector candidates to the candidate list in a predefined checking order until the maximum candidate list number is reached. This places a limit on the number of candidate vectors considered and hence decreases processing resource usage.

[0018] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein a most frequently used motion vector is inserted into the candidate list. This inserts a motion vector candidate that has repeatedly proven useful in encoding previous blocks, and is hence likely to provide a good approximation of the current block.

[0019] In an embodiment, the disclosure includes a video decoder comprises a receiver configured to receive a candidate list index in a bitstream. The video decoder also comprises a processor coupled to the receiver. The processor is configured to select a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block; apply the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block; determine a motion vector for the current block based on the candidate list of motion vectors and the candidate list index; and reconstruct the current block for display via a display device based on the motion vector. This approach selects from a group of patterns for generating a candidate list for inter-prediction instead of using a single pattern in all cases. This results in better compression when video blocks are encoded in an order other than raster order. Specifically, this approach determines the position of available (e.g., valid) coded blocks around the current block, and selects the pattern for candidate list generation based on such determination. This results in selecting patterns that have a high likelihood of including useful data to support block coding, and hence an increased likelihood of including a candidate vector that accurately describes motion of the current block.

[0020] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the candidate list is a merge candidate list or an AMVP candidate list.

[0021] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a top right corner, and a top left corner of the current block when the available coded blocks are positioned above the current block and left of the current block. This approach selects candidate motion vectors from the top and left of the current block when the available coded blocks are to the top and left of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0022] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and right of the current block. This approach selects candidate motion vectors from the top and right of the current block when the available coded blocks are to the top and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0023] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and below the current block. This approach selects candidate motion vectors from the top and bottom of the current block when the available coded blocks are to the top and bottom of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0024] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from above, left, and right of the current block when the available coded blocks are above, left, and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0025] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, below the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from all around the current block when the available coded blocks are all around the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0026] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; then checking blocks in a B position with a common reference index with the current block; and then checking blocks in a B position with a scaled reference index.

[0027] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; then checking blocks in an A position with a common reference index with the current block; and then checking blocks in an A position with a scaled reference index.

[0028] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index.

[0029] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0030] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index.

[0031] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0032] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the bitstream includes a maximum candidate list number, and wherein the selected candidate list determination pattern adds motion vector candidates to the candidate list in a predefined checking order until the maximum candidate list number is reached. This places a limit on the number of candidate vectors considered and hence decreases processing resource usage.

[0033] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein a most frequently used motion vector is inserted into the candidate list. This inserts a motion vector candidate that has repeatedly proven useful in encoding previous blocks, and is hence likely to provide a good approximation of the current block.

[0034] In an embodiment, the disclosure includes a non-transitory computer readable medium comprising a computer program product for use by a video decoder, the computer program product comprising computer executable instructions stored on the non-transitory computer readable medium such that when executed by a processor cause the video decoder to perform any of the methods described above.

[0035] In an embodiment, the disclosure includes a video decoder comprising: a receiving module for receiving a candidate list index in a bitstream; a pattern selection module for selecting a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block; a candidate list generation module for applying the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block; a motion vector determination module for determining a motion vector for the current block based on the candidate list of motion vectors and the candidate list index; and a reconstruction module for reconstructing the current block for display via a display device based on the motion vector. This approach selects from a group of patterns for generating a candidate list for inter- prediction instead of using a single pattern in all cases. This results in better compression when video blocks are encoded in an order other than raster order. Specifically, this approach determines the position of available (e.g., valid) coded blocks around the current block, and selects the pattern for candidate list generation based on such determination. This results in selecting patterns that have a high likelihood of including useful data to support block coding, and hence an increased likelihood of including a candidate vector that accurately describes motion of the current block.

[0036] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the receiving module, pattern selecting module, candidate list generation module, motion vector determination module, and reconstruction module are further for performing any of the methods described above.

[0037] In an embodiment, the disclosure includes a method implemented in a video encoder. The method comprises: selecting, by a processor in the video encoder, a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block; applying, by the processor, the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block; selecting, by the processor, a selected motion vector from the candidate list to encode the current block; encoding, by the processor, a candidate index corresponding to the selected motion vector in a bitstream; and transmitting, by a transmitter of the video encoder, the bitstream to support reconstruction of the current block for display at a video decoder. This approach selects from a group of patterns for generating a candidate list for inter-prediction instead of using a single pattern in all cases. This results in better compression when video blocks are encoded in an order other than raster order. Specifically, this approach determines the position of available (e.g., valid) coded blocks around the current block, and selects the pattern for candidate list generation based on such determination. This results in selecting patterns that have a high likelihood of including useful data to support block coding, and hence an increased likelihood of including a candidate vector that accurately describes motion of the current block.

[0038] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the candidate list is a merge candidate list or an AMVP candidate list.

[0039] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a top right corner, and a top left corner of the current block when the available coded blocks are positioned above the current block and left of the current block. This approach selects candidate motion vectors from the top and left of the current block when the available coded blocks are to the top and left of the current block, which ensures that the positions searched contain usable previously coded motion vectors. [0040] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and right of the current block. This approach selects candidate motion vectors from the top and right of the current block when the available coded blocks are to the top and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0041] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and below the current block. This approach selects candidate motion vectors from the top and bottom of the current block when the available coded blocks are to the top and bottom of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0042] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from above, left, and right of the current block when the available coded blocks are above, left, and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0043] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, below the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from all around the current block when the available coded blocks are all around the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0044] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; then checking blocks in a B position with a common reference index with the current block; and then checking blocks in a B position with a scaled reference index.

[0045] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; then checking blocks in an A position with a common reference index with the current block; and then checking blocks in an A position with a scaled reference index.

[0046] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index.

[0047] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0048] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index. [0049] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0050] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the bitstream includes a maximum candidate list number, and wherein the selected candidate list determination pattern adds motion vector candidates to the candidate list in a predefined checking order until the maximum candidate list number is reached. This places a limit on the number of candidate vectors considered and hence decreases processing resource usage.

[0051] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein a most frequently used motion vector is inserted into the candidate list. This inserts a motion vector candidate that has repeatedly proven useful in encoding previous blocks, and is hence likely to provide a good approximation of the current block.

[0052] In an embodiment, the disclosure includes a video encoder comprises a processor configured to: select a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block; apply the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block; select a selected motion vector from the candidate list to encode the current block; and encode a candidate index corresponding to the selected motion vector in a bitstream. The video encoder also comprises a transmitter coupled to the processor, the transmitter configured to transmit the bitstream to support reconstruction of the current block for display at a video decoder. This approach selects from a group of patterns for generating a candidate list for inter-prediction instead of using a single pattern in all cases. This results in better compression when video blocks are encoded in an order other than raster order. Specifically, this approach determines the position of available (e.g., valid) coded blocks around the current block, and selects the pattern for candidate list generation based on such determination. This results in selecting patterns that have a high likelihood of including useful data to support block coding, and hence an increased likelihood of including a candidate vector that accurately describes motion of the current block. [0053] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the candidate list is a merge candidate list or an AMVP candidate list.

[0054] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a top right corner, and a top left corner of the current block when the available coded blocks are positioned above the current block and left of the current block. This approach selects candidate motion vectors from the top and left of the current block when the available coded blocks are to the top and left of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0055] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and right of the current block. This approach selects candidate motion vectors from the top and right of the current block when the available coded blocks are to the top and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0056] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and below the current block. This approach selects candidate motion vectors from the top and bottom of the current block when the available coded blocks are to the top and bottom of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0057] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from above, left, and right of the current block when the available coded blocks are above, left, and right of the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0058] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, below the current block, left of the current block, and right of the current block. This approach selects candidate motion vectors from all around the current block when the available coded blocks are all around the current block, which ensures that the positions searched contain usable previously coded motion vectors.

[0059] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; then checking blocks in a B position with a common reference index with the current block; and then checking blocks in a B position with a scaled reference index.

[0060] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; then checking blocks in an A position with a common reference index with the current block; and then checking blocks in an A position with a scaled reference index.

[0061] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index.

[0062] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0063] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in a B position with a scaled reference index; and then checking blocks in an A position with a scaled reference index.

[0064] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the selected candidate list determination pattern searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. The predefined checking order includes: checking blocks in an A position with a common reference index with the current block; then checking blocks in a B position with a common reference index with the current block; then checking blocks in an A position with a scaled reference index; and then checking blocks in a B position with a scaled reference index.

[0065] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the bitstream includes a maximum candidate list number, and wherein the selected candidate list determination pattern adds motion vector candidates to the candidate list in a predefined checking order until the maximum candidate list number is reached. This places a limit on the number of candidate vectors considered and hence decreases processing resource usage.

[0066] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein a most frequently used motion vector is inserted into the candidate list. This inserts a motion vector candidate that has repeatedly proven useful in encoding previous blocks, and is hence likely to provide a good approximation of the current block.

[0067] In an embodiment, the disclosure includes a non-transitory computer readable medium comprising a computer program product for use by a video decoder, the computer program product comprising computer executable instructions stored on the non-transitory computer readable medium such that when executed by a processor cause the video decoder to perform any of the methods described above.

[0068] In an embodiment, the disclosure includes a video encoder comprising: a pattern selection module for selecting a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block; a candidate list generation module for applying the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block; a motion vector selection module for selecting a selected motion vector from the candidate list to encode the current block; an encoding module for encoding a candidate index corresponding to the selected motion vector in a bitstream; and a transmitter module for transmitting the bitstream to support reconstruction of the current block for display at a video decoder. This approach selects from a group of patterns for generating a candidate list for inter- prediction instead of using a single pattern in all cases. This results in better compression when video blocks are encoded in an order other than raster order. Specifically, this approach determines the position of available (e.g., valid) coded blocks around the current block, and selects the pattern for candidate list generation based on such determination. This results in selecting patterns that have a high likelihood of including useful data to support block coding, and hence an increased likelihood of including a candidate vector that accurately describes motion of the current block.

[0069] Optionally, in any of the preceding aspects, another implementation of the aspect includes, wherein the pattern selection module, candidate list generation module, motion vector selection module, encoding module, and transmitter module are further for performing any of the methods above.

[0070] For the purpose of clarity, any one of the foregoing embodiments may be combined with any one or more of the other foregoing embodiments to create a new embodiment within the scope of the present disclosure.

[0071] These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0073] FIG. 1 is a flowchart of an example method of coding a video signal.

[0074] FIG. 2 is a schematic diagram of an example coding and decoding (codec) system for video coding. [0075] FIG. 3 is a schematic diagram illustrating an example video encoder that may select a candidate list determination pattern based on available coded block position.

[0076] FIG. 4 is a schematic diagram illustrating an example video decoder that may select a candidate list determination pattern based on available coded block position.

[0077] FIG. 5 is a schematic diagram illustrating an example of unidirectional inter- prediction.

[0078] FIG. 6 is a schematic diagram illustrating an example of bidirectional inter- prediction.

[0079] FIG. 7 is a schematic diagram illustrating a first example available coded block position.

[0080] FIG. 8 is a schematic diagram illustrating an example candidate list determination pattern selected based on the first example available coded block position.

[0081] FIG. 9 is a schematic diagram illustrating a second example available coded block position.

[0082] FIG. 10 is a schematic diagram illustrating an example candidate list determination pattern selected based on the second example available coded block position.

[0083] FIG. 11 is a schematic diagram illustrating a third example available coded block position.

[0084] FIG. 12 is a schematic diagram illustrating an example candidate list determination pattern selected based on the third example available coded block position.

[0085] FIG. 13 is a schematic diagram illustrating a fourth example available coded block position.

[0086] FIG. 14 is a schematic diagram illustrating an example candidate list determination pattern selected based on the fourth example available coded block position.

[0087] FIG. 15 is a schematic diagram illustrating another example candidate list determination pattern selected based on the fourth example available coded block position.

[0088] FIG. 16 is a schematic diagram illustrating a fifth example available coded block position.

[0089] FIG. 17 is a schematic diagram illustrating an example candidate list determination pattern selected based on the fifth example available coded block position.

[0090] FIG. 18 is a flowchart of an example method of selecting a candidate list determination pattern based on available coded block position at an encoder.

[0091] FIG. 19 is a flowchart of an example method of selecting a candidate list determination pattern based on available coded block position at a decoder. [0092] FIG. 20 is a schematic diagram of an example video coding device.

[0093] FIG. 21 is a schematic diagram of example devices for selecting a candidate list determination pattern based on available coded block position.

DETAILED DESCRIPTION

[0094] It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

[0095] Video coding involves a combination of compression by inter-prediction and intra- prediction. The present disclosure focuses on increasing the coding efficiency of inter- prediction, which is a mechanism to encode the position of an object in a frame based on the position of the object in a different frame. For example, a motion vector can indicate a direction of movement of an object over time as depicted over multiple frames of a sequence of video. Hence, an object in a reference frame and a motion vector can be encoded and then employed by a decoder to partially reconstruct one or more frames that are temporally adjacent to the reference frame. Inter-prediction can employ unidirectional inter-prediction and/or bidirectional inter-prediction. Unidirectional inter-prediction uses a single motion vector to a single reference frame to predict the location of an object in a current frame. Bidirectional inter-prediction uses a preceding motion vector pointing towards a preceding reference frame and a subsequent motion vector pointing towards a subsequent reference frame.

[0096] Inter-prediction can be accomplished according to several modes. For example, inter-prediction can be accomplished according to merge mode. In merge mode, an encoder generates a candidate list of motion vectors for a current block by obtaining motion vectors used for previously coded neighboring blocks. A neighboring block is a block that is spatially or temporally adjacent to the current block. The encoder then selects a motion vector for the current block from the candidate list. The encoder can then determine an index for the selected motion vector in the candidate list. The encoder encodes the current block in a bitstream as the index and residual data (if any) indicating the difference between a reference block and the current block. On the decoder side, the decoder generates the candidate list of motion vectors by employing the same process as the encoder. The decoder can then determine the motion vector based on the signaled index and employ the motion vector, the reference block for the motion vector, and the residual data to reconstruct the current block. As another example, inter- prediction can also be accomplished according to adaptive motion vector prediction (AMVP) mode. AMVP is similar to merge mode, except the encoder is not restricted to using one or the motion vectors from the candidate list. In AMVP mode, the encoder can select a motion vector for the current block. The encoder can then select a candidate motion vector from the candidate list that most closely reflects the selected motion vector. The encoder then encodes the current block as the candidate list index of the selected candidate motion vector, the difference between the selected candidate motion vector and the selected motion vector for the current block, and residual data (if any). The decoder can determine the selected candidate motion vector based on the index and determine the selected motion vector for the current block based on the difference between the selected motion vector and the selected candidate motion vector. The decoder can then reconstruct the current block based on the selected motion vector, the reference block for the selected motion vector, and the residual data.

[0097] In many video coding systems, coding proceeds in raster order from the left side of the frame to the right side and from the top of the frame to the bottom of the frame. In such systems merge mode and AMVP mode use a consistent pattern to determine the candidate list. The pattern used is employed to take advantage of the coding order. However, other coding orders are possible, such as from the right side of the frame to the left side and from the bottom of the frame to the top of the frame. In the event that an alternate coding order is employed, the pattern used for determining the candidate list may provide sub-optimal results. For example, merge mode and AMVP mode may generate the candidate list based on coded neighbor blocks positioned above and/or to the left of the current block. In the event of an alternate coding order, such blocks may not be coded when the candidate list is generated for the current block. In such a case, the encoder may have a very limited number of candidate motion vectors to choose from. This could cause an inefficient coding to be selected, which would increase the size of the final encoded bitstream. For example, in AMVP mode a poor candidate motion vector selection may result in encoding a large value for the difference between the selected motion vector and the selected candidate motion vector. As another example, in merge mode a poor candidate motion vector selection may result in a sub-optimal reference block, and hence a significantly increased amount or residual data that is encoded to reconstruct the current block.

[0098] Disclosed herein are mechanisms to select a candidate list determination pattern based on available coded block position. This approach allows for generation of an optimized candidate list regardless of the coding order. Specifically, different candidate list determination patterns can be selected depending on the location of the coded neighbor blocks. In a first example, a selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a top right corner, and a top left corner of the current block when the available coded blocks are positioned above the current block and left of the current block. In a second example, the selected candidate list determination pattern searches available coded blocks adjacent to a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and right of the current block. In a third example, the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block and below the current block. In a fourth example, the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, left of the current block, and right of the current block. In a fifth example, the selected candidate list determination pattern searches available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block when the available coded blocks are positioned above the current block, below the current block, left of the current block, and right of the current block. Further, the preceding examples can each search the available coded blocks in several checking orders described in more detail below.

[0099] FIG. 1 is a flowchart of an example operating method 100 of coding a video signal. Specifically, a video signal is encoded at an encoder. The encoding process compresses the video signal by employing various mechanisms to reduce the video file size. A smaller file size allows the compressed video file to be transmitted toward a user, while reducing associated bandwidth overhead. The decoder then decodes the compressed video file to reconstruct the original video signal for display to an end user. The decoding process generally mirrors the encoding process to allow the decoder to consistently reconstruct the video signal.

[00100] At step 101, the video signal is input into the encoder. For example, the video signal may be an uncompressed video file stored in memory. As another example, the video file may be captured by a video capture device, such as a video camera, and encoded to support live streaming of the video. The video file may include both an audio component and a video component. The video component contains a series of image frames that, when viewed in a sequence, gives the visual impression of motion. The frames contain pixels that are expressed in terms of light, referred to herein as luma components, and color, which is referred to as chroma components. In some examples, the frames may also contain depth values to support three dimensional viewing.

[00101] At step 103, the video is partitioned into blocks. Partitioning includes subdividing the pixels in each frame into square and/or rectangular blocks for compression. For example, coding trees may be employed to divide and then recursively subdivide blocks until configurations are achieved that support further encoding. As such, the blocks may be referred to as coding tree units in High Efficiency Video Coding (HEVC) (also known as H.265 and MPEG-H Part 2). For example, luma components of a frame may be subdivided until the individual blocks contain relatively homogenous lighting values. Further, chroma components of a frame may be subdivided until the individual blocks contain relatively homogenous color values. Accordingly, partitioning mechanisms vary depending on the content of the video frames.

[00102] At step 105, various compression mechanisms are employed to compress the image blocks partitioned at step 103. For example, inter-prediction and/or intra-prediction may be employed. Inter-prediction is designed to take advantage of the fact that objects in a common scene tend to appear in successive frames. Accordingly, a block depicting an object in a reference frame need not be repeatedly described in adjacent frames. Specifically, an object, such as a table, may remain in a constant position over multiple frames. Hence the table is described once and adjacent frames can refer back to the reference frame. Pattern matching mechanisms may be employed to match objects over multiple frames. Further, moving objects may be represented across multiple frames, for example due to object movement or camera movement. As a particular example, a video may show an automobile that moves across the screen over multiple frames. Motion vectors can be employed to describe such movement. A motion vector is a two-dimensional vector that provides an offset from the coordinates of an object in a frame to the coordinates of the object in a reference frame. As such, inter-prediction can encode an image block in a current frame as a set of motion vectors indicating an offset from a corresponding block in a reference frame.

[00103] Intra-prediction encodes blocks in a common frame. Intra-prediction takes advantage of the fact that luma and chroma components tend to cluster in a frame. For example, a patch of green in a portion of a tree tends to be positioned adjacent to similar patches of green. Intra-prediction employs multiple directional prediction modes (e.g., thirty three in HEVC), a planar mode, and a direct current (DC) mode. The directional modes indicate that a current block is similar/the same as samples of a neighbor block in a corresponding direction. Planar mode indicates that a series of blocks along a row/column (e.g., a plane) can be interpolated based on neighbor blocks at the edges of the row. Planar mode, in effect, indicates a smooth transition of light/color across a row/column by employing a relatively constant slope in changing values. DC mode is employed for boundary smoothing and indicates that a block is similar/the same as an average value associated with samples of all the neighbor blocks associated with the angular directions of the directional prediction modes. Accordingly, intra-prediction blocks can represent image blocks as various relational prediction mode values instead of the actual values. Further, inter-prediction blocks can represent image blocks as motion vector values instead of the actual values. In either case, the prediction blocks may not exactly represent the image blocks in some cases. Any differences are stored in residual blocks. Transforms may be applied to the residual blocks to further compress the file.

[00104] At step 107, various filtering techniques may be applied. In HEVC, the filters are applied according to an in-loop filtering scheme. The block based prediction discussed above may result in the creation of blocky images at the decoder. Further, the block based prediction scheme may encode a block and then reconstruct the encoded block for later use as a reference block. The in-loop filtering scheme iteratively applies noise suppression filters, de-blocking filters, adaptive loop filters, and sample adaptive offset (SAO) filters to the blocks/frames. These filters mitigate such blocking artifacts so that the encoded file can be accurately reconstructed. Further, these filters mitigate artifacts in the reconstructed reference blocks so that artifacts are less likely to create additional artifacts in subsequent blocks that are encoded based on the reconstructed reference blocks.

[00105] Once the video signal has been partitioned, compressed, and filtered, the resulting data is encoded in a bitstream at step 109. The bitstream includes the data discussed above as well as any signaling data desired to support proper video signal reconstruction at the decoder. For example, such data may include partition data, prediction data, residual blocks, and various flags providing coding instructions to the decoder. The bitstream may be stored in memory for transmission toward a decoder upon request. The bitstream may also be broadcast and/or multicast toward a plurality of decoders. The creation of the bitstream is an iterative process. Accordingly, steps 101, 103, 105, 107, and 109 may occur continuously and/or simultaneously over many frames and blocks. The order shown in FIG. 1 is presented for clarity and ease of discussion, and is not intended to limit the video coding process to a particular order.

[00106] The decoder receives the bitstream and begins the decoding process at step 111. Specifically, the decoder employs an entropy decoding scheme to convert the bitstream into corresponding syntax and video data. The decoder employs the syntax data from the bitstream to determine the partitions for the frames at step 111. The partitioning should match the results of block partitioning at step 103. Entropy encoding/decoding as employed in step 11 1 is now described. The encoder makes many choices during the compression process, such as selecting block partitioning schemes from several possible choices based on the spatial positioning of values in the input image(s). Signaling the exact choices may employ a large number of bins. As used herein, a bin is a binary value that is treated as a variable (e.g., a bit value that may vary depending on context). Entropy coding allows the encoder to discard any options that are clearly not viable for a particular case, leaving a set of allowable options. Each allowable option is then assigned a code word. The length of the code words is based on the number of allowable options (e.g., one bin for two options, two bins for three to four options, etc.) The encoder then encodes the code word for the selected option. This scheme reduces the size of the code words as the code words are as big as desired to uniquely indicate a selection from a small sub-set of allowable options as opposed to uniquely indicating the selection from a potentially large set of all possible options. The decoder then decodes the selection by determining the set of allowable options in a similar manner to the encoder. By determining the set of allowable options, the decoder can read the code word and determine the selection made by the encoder.

[00107] At step 113, the decoder performs block decoding. Specifically, the decoder employs reverse transforms to generate residual blocks. Then the decoder employs the residual blocks and corresponding prediction blocks to reconstruct the image blocks according to the partitioning. The prediction blocks may include both intra-prediction blocks and inter- prediction blocks as generated at the encoder at step 105. The reconstructed image blocks are then positioned into frames of a reconstructed video signal according to the partitioning data determined at step 111. Syntax for step 113 may also be signaled in the bitstream via entropy coding as discussed above.

[00108] At step 115, filtering is performed on the frames of the reconstructed video signal in a manner similar to step 107 at the encoder. For example, noise suppression filters, deblocking filters, adaptive loop filters, and SAO filters may be applied to the frames to remove blocking artifacts. Once the frames are filtered, the video signal can be output to a display at step 117 for viewing by an end user.

[00109] The present disclosure relates to modifications to provide for increased coding efficiency when performing inter-prediction via merge mode and AMVP mode. Specifically, the present disclosure introduces a mechanism to select, by a processor in the video decoder, a selected candidate list determination pattern based on available coded blocks around a current block. This increases coding efficiency and hence reduces the file size of an encoded bitstream when blocks are coded in non-raster order. As used herein, non-raster order is any spatial order other than left to right and top to bottom with respect to a video frame. Hence, the inter- prediction mechanisms described in the FIGS, below impact the operation of block compression at step 105, bitstream encoding and transmission at step 109, and block decoding at step 113.

[00110] FIG. 2 is a schematic diagram of an example coding and decoding (codec) system 200 for video coding. Specifically, codec system 200 provides functionality to support the implementation of operating method 100. Codec system 200 is generalized to depict components employed in both an encoder and a decoder. Codec system 200 receives and partitions a video signal as discussed with respect to steps 101 and 103 in operating method 100, which results in a partitioned video signal 201. Codec system 200 then compresses the partitioned video signal 201 into a coded bitstream when acting as an encoder as discussed with respect to steps 105, 107, and 109 in method 100. When acting as a decoder codec system 200 generates an output video signal from the bitstream as discussed with respect to steps 111, 113, 115, and 117 in operating method 100. The codec system 200 includes a general coder control component 211, a transform scaling and quantization component 213, an intra-picture estimation component 215, an intra-picture prediction component 217, a motion compensation component 219, a motion estimation component 221, a scaling and inverse transform component 229, a filter control analysis component 227, an in-loop filters component 225, a decoded picture buffer component 223, and a header formatting and context adaptive binary arithmetic coding (CAB AC) component 231. Such components are coupled as shown. In FIG. 2, black lines indicate movement of data to be encoded/decoded while dashed lines indicate movement of control data that controls the operation of other components. The components of codec system 200 may all be present in the encoder. The decoder may include a subset of the components of codec system 200. For example, the decoder may include the intra-picture prediction component 217, the motion compensation component 219, the scaling and inverse transform component 229, the in-loop filters component 225, and the decoded picture buffer component 223. These components are now described.

[00111] The partitioned video signal 201 is a captured video sequence that has been partitioned into blocks of pixels by a coding tree. A coding tree employs various split modes to subdivide a block of pixels into smaller blocks of pixels. These blocks can then be further subdivided into smaller blocks. The blocks may be referred to as nodes on the coding tree. Larger parent nodes are split into smaller child nodes. The number of times a node is subdivided is referred to as the depth of the node/coding tree. The divided blocks are referred to as coding units (CUs) in some cases. The split modes may include a binary tree (BT), triple tree (TT), and a quad tree (QT) employed to partition a node into two, three, or four child nodes, respectively, of varying shapes depending on the split modes employed. The partitioned video signal 201 is forwarded to the general coder control component 211, the transform scaling and quantization component 213, the intra-picture estimation component 215, the filter control analysis component 227, and the motion estimation component 221 for compression.

[00112] The general coder control component 211 is configured to make decisions related to coding of the images of the video sequence into the bitstream according to application constraints. For example, the general coder control component 211 manages optimization of bitrate/bitstream size versus reconstruction quality. Such decisions may be made based on storage space/bandwidth availability and image resolution requests. The general coder control component 211 also manages buffer utilization in light of transmission speed to mitigate buffer underrun and overrun issues. To manage these issues, the general coder control component 21 1 manages partitioning, prediction, and filtering by the other components. For example, the general coder control component 211 may dynamically increase compression complexity to increase resolution and increase bandwidth usage or decrease compression complexity to decrease resolution and bandwidth usage. Hence, the general coder control component 211 controls the other components of codec system 200 to balance video signal reconstruction quality with bit rate concerns. The general coder control component 211 creates control data, which controls the operation of the other components. The control data is also forwarded to the header formatting and CABAC component 231 to be encoded in the bitstream to signal parameters for decoding at the decoder.

[00113] The partitioned video signal 201 is also sent to the motion estimation component 221 and the motion compensation component 219 for inter-prediction. A frame or slice of the partitioned video signal 201 may be divided into multiple video blocks. Motion estimation component 221 and the motion compensation component 219 perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference frames to provide temporal prediction. Codec system 200 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.

[00114] Motion estimation component 221 and motion compensation component 219 may be highly integrated, but are illustrated separately for conceptual purposes. Motion estimation, performed by motion estimation component 221, is the process of generating motion vectors, which estimate motion for video blocks. A motion vector, for example, may indicate the displacement of a coded object relative to a predictive block. A predictive block is a block that is found to closely match the block to be coded, in terms of pixel difference. A predictive block may also be referred to as a reference block. Such pixel difference may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. HEVC employs several coded objects including a coding tree unit (CTU), coding tree blocks (CTBs), and CUs. For example, a CTU can be divided into CTBs, which can then be divided into CUs, which can be further sub-divided as desired. A CU can be encoded as a prediction unit (PU) containing prediction data and/or a transform unit (TU) containing transformed residual data for the CU. The motion estimation component 221 generates motion vectors, PUs, and TUs by using a rate-distortion analysis as part of a rate distortion optimization process. For example, the motion estimation component 221 may determine multiple reference blocks, multiple motion vectors, etc. for a current block/frame, and may select the reference blocks, motion vectors, etc. having the best rate-distortion characteristics. The best rate-distortion characteristics balance both quality of video reconstruction (e.g., amount of data loss by compression) with coding efficiency (e.g., size of the final encoding).

[00115] In some examples, codec system 200 may calculate values for sub-integer pixel positions of reference pictures stored in decoded picture buffer component 223. For example, video codec system 200 may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference picture. Therefore, motion estimation component 221 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision. The motion estimation component 221 calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU to the position of a predictive block of a reference picture. Motion estimation component 221 outputs the calculated motion vector as motion data to header formatting and CABAC component 231 for encoding and motion to the motion compensation component 219.

[00116] Motion compensation, performed by motion compensation component 219, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation component 221. Again, motion estimation component 221 and motion compensation component 219 may be functionally integrated, in some examples. Upon receiving the motion vector for the PU of the current video block, motion compensation component 219 may locate the predictive block to which the motion vector points. A residual video block is then formed by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values. In general, motion estimation component 221 performs motion estimation relative to luma components, and motion compensation component 219 uses motion vectors calculated based on the luma components for both chroma components and luma components. The predictive block and residual block are forwarded to transform scaling and quantization component 213.

[00117] The partitioned video signal 201 is also sent to intra-picture estimation component 215 and intra-picture prediction component 217. As with motion estimation component 221 and motion compensation component 219, intra-picture estimation component 215 and intra- picture prediction component 217 may be highly integrated, but are illustrated separately for conceptual purposes. The intra-picture estimation component 215 and intra-picture prediction component 217 intra-predict a current block relative to blocks in a current frame, as an alternative to the inter-prediction performed by motion estimation component 221 and motion compensation component 219 between frames, as described above. In particular, the intra- picture estimation component 215 determines an intra-prediction mode to use to encode a current block. In some examples, intra-picture estimation component 215 selects an appropriate intra-prediction mode to encode a current block from multiple tested intra- prediction modes. The selected intra-prediction modes are then forwarded to the header formatting and CAB AC component 231 for encoding.

[00118] For example, the intra-picture estimation component 215 calculates rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and selects the intra-prediction mode having the best rate-distortion characteristics among the tested modes. Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original unencoded block that was encoded to produce the encoded block, as well as a bitrate (e.g., a number of bits) used to produce the encoded block. The intra-picture estimation component 215 calculates ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate- distortion value for the block. In addition, intra-picture estimation component 215 may be configured to code depth blocks of a depth map using a depth modeling mode (DMM) based on rate-distortion optimization (RDO).

[00119] The intra-picture prediction component 217 may generate a residual block from the predictive block based on the selected intra-prediction modes determined by intra-picture estimation component 215 when implemented on an encoder or read the residual block from the bitstream when implemented on a decoder. The residual block includes the difference in values between the predictive block and the original block, represented as a matrix. The residual block is then forwarded to the transform scaling and quantization component 213. The intra-picture estimation component 215 and the intra-picture prediction component 217 may operate on both luma and chroma components.

[00120] The transform scaling and quantization component 213 is configured to further compress the residual block. The transform scaling and quantization component 213 applies a transform, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to the residual block, producing a video block comprising residual transform coefficient values. Wavelet transforms, integer transforms, sub-band transforms or other types of transforms could also be used. The transform may convert the residual information from a pixel value domain to a transform domain, such as a frequency domain. The transform scaling and quantization component 213 is also configured to scale the transformed residual information, for example based on frequency. Such scaling involves applying a scale factor to the residual information so that different frequency information is quantized at different granularities, which may affect final visual quality of the reconstructed video. The transform scaling and quantization component 213 is also configured to quantize the transform coefficients to further reduce bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, the transform scaling and quantization component 213 may then perform a scan of the matrix including the quantized transform coefficients. The quantized transform coefficients are forwarded to the header formatting and CAB AC component 231 to be encoded in the bitstream.

[00121] The scaling and inverse transform component 229 applies a reverse operation of the transform scaling and quantization component 213 to support motion estimation. The scaling and inverse transform component 229 applies inverse scaling, transformation, and/or quantization to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block which may become a predictive block for another current block. The motion estimation component 221 and/or motion compensation component 219 may calculate a reference block by adding the residual block back to a corresponding predictive block for use in motion estimation of a later block/frame. Filters are applied to the reconstructed reference blocks to mitigate artifacts created during scaling, quantization, and transform. Such artifacts could otherwise cause inaccurate prediction (and create additional artifacts) when subsequent blocks are predicted.

[00122] The filter control analysis component 227 and the in-loop filters component 225 apply the filters to the residual blocks and/or to reconstructed image blocks. For example, the transformed residual block from scaling and inverse transform component 229 may be combined with a corresponding prediction block from intra-picture prediction component 217 and/or motion compensation component 219 to reconstruct the original image block. The filters may then be applied to the reconstructed image block. In some examples, the filters may instead be applied to the residual blocks. As with other components in FIG. 2, the filter control analysis component 227 and the in-loop filters component 225 are highly integrated and may be implemented together, but are depicted separately for conceptual purposes. Filters applied to the reconstructed reference blocks are applied to particular spatial regions and include multiple parameters to adjust how such filters are applied. The filter control analysis component 227 analyzes the reconstructed reference blocks to determine where such filters should be applied and sets corresponding parameters. Such data is forwarded to the header formatting and CABAC component 231 as filter control data for encoding. The in-loop filters component 225 applies such filters based on the filter control data. The filters may include a deblocking filter, a noise suppression filter, a SAO filter, and an adaptive loop filter. Such filters may be applied in the spatial/pixel domain (e.g., on a reconstructed pixel block) or in the frequency domain, depending on the example.

[00123] When operating as an encoder, the filtered reconstructed image block, residual block, and/or prediction block are stored in the decoded picture buffer component 223 for later use in motion estimation as discussed above. When operating as a decoder, the decoded picture buffer component 223 stores and forwards the reconstructed and filtered blocks toward a display as part of an output video signal. The decoded picture buffer component 223 may be any memory device capable of storing prediction blocks, residual blocks, and/or reconstructed image blocks.

[00124] The header formatting and CABAC component 231 receives the data from the various components of codec system 200 and encodes such data into a coded bitstream for transmission toward a decoder. Specifically, the header formatting and CABAC component 231 generates various headers to encode control data, such as general control data and filter control data. Further, prediction data, including intra-prediction and motion data, as well as residual data in the form of quantized transform coefficient data are all encoded in the bitstream. The final bitstream includes all information desired by the decoder to reconstruct the original partitioned video signal 201. Such information may also include intra-prediction mode index tables (also referred to as codeword mapping tables), definitions of encoding contexts for various blocks, indications of most probable intra-prediction modes, an indication of partition information, etc. Such data may be encoded be employing entropy coding. For example, the information may be encoded by employing context adaptive variable length coding (CAVLC), CABAC, syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy coding technique. Following the entropy coding, the coded bitstream may be transmitted to another device (e.g., a video decoder) or archived for later transmission or retrieval.

[00125] The present disclosure includes modifications to provide for increased coding efficiency when performing inter-prediction via merge mode and AMVP mode. Specifically, the present disclosure introduces a mechanism for selecting, by a processor in the video decoder, a candidate list determination pattern based on available coded blocks around a current block. This increases coding efficiency and hence reduces the file size of an encoded bitstream when blocks are coded in non-raster order. Hence, the inter-prediction mechanisms described in the FIGS, below impact the operation of motion estimation component 221, motion compensation component 219, and/or header formatting and CABAC component 231.

[00126] FIG. 3 is a block diagram illustrating an example video encoder 300 that may select a candidate list determination pattern based on available coded block position. Video encoder 300 may be employed to implement the encoding functions of codec system 200 and/or implement steps 101, 103, 105, 107, and/or 109 of operating method 100. Encoder 300 partitions an input video signal, resulting in a partitioned video signal 301, which is substantially similar to the partitioned video signal 201. The partitioned video signal 301 is then compressed and encoded into a bitstream by components of encoder 300.

[00127] Specifically, the partitioned video signal 301 is forwarded to an intra-picture prediction component 317 for intra-prediction. The intra-picture prediction component 317 may be substantially similar to intra-picture estimation component 215 and intra-picture prediction component 217. The partitioned video signal 301 is also forwarded to a motion compensation component 321 for inter-prediction based on reference blocks in a decoded picture buffer component 323. The motion compensation component 321 may be substantially similar to motion estimation component 221 and motion compensation component 219. The prediction blocks and residual blocks from the intra-picture prediction component 317 and the motion compensation component 321 are forwarded to a transform and quantization component 313 for transform and quantization of the residual blocks. The transform and quantization component 313 may be substantially similar to the transform scaling and quantization component 213. The transformed and quantized residual blocks and the corresponding prediction blocks (along with associated control data) are forwarded to an entropy coding component 331 for coding into a bitstream. The entropy coding component 331 may be substantially similar to the header formatting and CABAC component 231. [00128] The transformed and quantized residual blocks and/or the corresponding prediction blocks are also forwarded from the transform and quantization component 313 to an inverse transform and quantization component 329 for reconstruction into reference blocks for use by the motion compensation component 321. The inverse transform and quantization component 329 may be substantially similar to the scaling and inverse transform component 229. In-loop filters in an in-loop filters component 325 are also applied to the residual blocks and/or reconstructed reference blocks, depending on the example. The in-loop filters component 325 may be substantially similar to the filter control analysis component 227 and the in-loop filters component 225. The in-loop filters component 325 may include multiple filters as discussed with respect to in-loop filters component 225. The filtered blocks are then stored in a decoded picture buffer component 323 for use as reference blocks by the motion compensation component 321. The decoded picture buffer component 323 may be substantially similar to the decoded picture buffer component 223.

[00129] The motion compensation component 321 can perform inter-prediction in several modes including merge mode and AMVP mode. The motion compensation component 321 operates on a current block according to rate distortion optimization. This includes attempting to encode the current block using multiple modes. The motion compensation component 321 selects the mode that provides the best tradeoff between picture quality loss due to encoding and coding efficiency resulting in greater compression. The motion compensation component 321 can attempt both merge mode and AMVP mode when determining the most optimal tradeoff.

[00130] In merge mode, the motion compensation component 321 generates a candidate list of motion vectors for a current block by obtaining motion vectors used for previously coded neighboring blocks. The motion compensation component 321 then selects a motion vector for the current block from the candidate list. The selected motion vector is the motion vector that corresponds to a reference block that most closely matches the current block being encoded. The motion compensation component 321 then determines an index for the selected motion vector in the candidate list. The motion compensation component 321 can then forward the candidate list index to the entropy coding component 331 for encoding in the bitstream along with any residual data indicating the difference between the reference block and the current block.

[00131] In AMVP mode, the motion compensation component 321 generates a candidate list of motion vectors for a current block by obtaining motion vectors used for previously coded neighboring blocks as in merge mode. The motion compensation component 321 selects a motion vector for the current block. The motion compensation component 321 then selects a motion vector that most closely reflects the selected motion vector. For example, the motion compensation component 321 may select a candidate motion vector based on similarity of the reference block between the candidate motion vector and the selected motion vector. Further, the motion compensation component 321 may select the candidate motion vector based on numerical similarity of between the candidate motion vector and the selected motion vector. The motion compensation component 321 then forwards the candidate list index of the selected candidate motion vector and the difference between the selected candidate motion vector and the selected motion vector for the current block to the entropy coding component 331 for encoding in the bitstream along with any residual data indicating the difference between the reference block and the current block.

[00132] In both merge mode and AMVP mode, the motion compensation component 321 generates a candidate list by adding candidate motion vectors to the candidate list in an order defined by a candidate list determination pattern. The candidate list determination pattern is selected depending on the location of the coded neighbor blocks. Examples of candidate list determination patterns and available coded block positions employed to select the candidate list determination patterns are disclosed with respect to the FIGS, below.

[00133] FIG. 4 is a block diagram illustrating an example video decoder 400 that may generate a motion model candidate list for inter-prediction. Video decoder 400 may be employed to implement the decoding functions of codec system 200 and/or implement steps 111, 113, 115, and/or 117 of operating method 100. Decoder 400 receives a bitstream, for example from an encoder 300, and generates a reconstructed output video signal based on the bitstream for display to an end user.

[00134] The bitstream is received by an entropy decoding component 433. The entropy decoding component 433 is configured to implement an entropy decoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or other entropy coding techniques. For example, the entropy decoding component 433 may employ header information to provide a context to interpret additional data encoded as codewords in the bitstream. The decoded information includes any desired information to decode the video signal, such as general control data, filter control data, partition information, motion data, prediction data, and quantized transform coefficients from residual blocks. The quantized transform coefficients are forwarded to an inverse transform and quantization component 429 for reconstruction into residual blocks. The inverse transform and quantization component 429 may be similar to inverse transform and quantization component 329. [00135] The reconstructed residual blocks and/or prediction blocks are forwarded to intra- picture prediction component 417 for reconstruction into image blocks based on intra- prediction operations. The intra-picture prediction component 417 may be similar to intra- picture estimation component 215 and an intra-picture prediction component 217. Specifically, the intra-picture prediction component 417 employs prediction modes to locate a reference block in the frame and applies a residual block to the result to reconstruct intra-predicted image blocks. The reconstructed intra-predicted image blocks and/or the residual blocks and corresponding inter-prediction data are forwarded to a decoded picture buffer component 423 via an in-loop filters component 425, which may be substantially similar to decoded picture buffer component 223 and in-loop filters component 225, respectively. The in-loop filters component 425 filters the reconstructed image blocks, residual blocks and/or prediction blocks, and such information is stored in the decoded picture buffer component 423. Reconstructed image blocks from decoded picture buffer component 423 are forwarded to a motion compensation component 421 for inter-prediction. The motion compensation component 421 may be substantially similar to motion estimation component 221 and/or motion compensation component 219. Specifically, the motion compensation component 421 employs motion vectors from a reference block to generate a prediction block and applies a residual block to the result to reconstruct an image block. The resulting reconstructed blocks may also be forwarded via the in-loop filters component 425 to the decoded picture buffer component 423. The decoded picture buffer component 423 continues to store additional reconstructed image blocks, which can be reconstructed into frames via the partition information. Such frames may also be placed in a sequence. The sequence is output toward a display as a reconstructed output video signal.

[00136] Like the video encoder 300, the video decoder 400 performs inter-prediction in several modes including merge mode and AMVP mode. In merge mode, the motion compensation component 421 generates the candidate list using the same mechanism as the motion compensation component 321. The motion compensation component 421 then employs the candidate list index from the bitstream to obtain the selected motion vector from the candidate list. In AMVP mode, the motion compensation component 421 also adjusts the selected candidate motion vector based on the difference between the selected candidate motion vector and the selected motion vector as encoded in the bitstream. In either case, the motion compensation component 421 reconstructs the current block based on the reference block indicated by the selected motion vector. The motion compensation component 421 then adjusts the current block based on any residual data to obtain a reconstructed current block that matches the block as encoded at the encoder 300.

[00137] In both merge mode and AMVP mode, the motion compensation component 421 generates a candidate list by adding candidate motion vectors to the candidate list in an order defined by a candidate list determination pattern. The candidate list determination pattern is selected depending on the location of the coded neighbor blocks. Examples of candidate list determination patterns and available coded block positions employed to select the candidate list determination patterns are disclosed with respect to the FIGS, below.

[00138] FIG. 5 is a schematic diagram illustrating an example of unidirectional inter- prediction 500, for example as performed to determine motion vectors (MVs) at block compression step 105, block decoding step 113, motion estimation component 221, motion compensation component 219, motion compensation component 321, and/or motion compensation component 421. For example, unidirectional inter-prediction 500 can be employed to determine motion vectors for a block in inter-prediction modes.

[00139] Unidirectional inter-prediction 500 employs a reference frame 530 with a reference block 531 to predict a current block 511 in a current frame 510. The reference frame 530 may be temporally positioned after the current frame 510 as shown (e.g., as a subsequent reference frame), but may also be temporally positioned before the current frame 510 (e.g., as a preceding reference frame) in some examples. The current frame 510 is an example frame/picture being encoded/decoded at a particular time. The current frame 510 contains an object in the current block 511 that matches an object in the reference block 531 of the reference frame 530. The reference frame 530 is a frame that is employed as a reference for encoding a current frame 510, and a reference block 531 is a block in the reference frame 530 that contains an object also contained in the current block 511 of the current frame 510.

[00140] The current block 511 is any coding unit that is being encoded/decoded at a specified point in the coding process. The current block 511 may be an entire partitioned block, or may be a sub-block in the affine inter-prediction case. The current frame 510 is separated from the reference frame 530 by some temporal distance (TD) 533. The TD 533 indicates an amount of time between the current frame 510 and the reference frame 530 in a video sequence, and may be measured in units of frames. The prediction information for the current block 511 may reference the reference frame 530 and/or reference block 531 by a reference index indicating the direction and temporal distance between the frames. Over the time period represented by the TD 533, the object in the current block 511 moves from a position in the current frame 510 to another position in the reference frame 530 (e.g., the position of the reference block 531). For example, the object may move along a motion trajectory 513, which is a direction of movement of an object over time. A motion vector 535 describes the direction and magnitude of the movement of the object along the motion trajectory 513 over the TD 533. Accordingly, an encoded motion vector 535 and a reference block 531 provides information sufficient to reconstruct a current block 511 and position the current block 511 in the current frame 510.

[00141] FIG. 6 is a schematic diagram illustrating an example of bidirectional inter- prediction 600, for example as performed to determine MVs at block compression step 105, block decoding step 113, motion estimation component 221, motion compensation component 219, motion compensation component 321, and/or motion compensation component 421. For example, bidirectional inter-prediction 600 can be employed to determine motion vectors for a block in inter-prediction modes and/or to determine motion vectors for sub-blocks in affine inter-prediction mode.

[00142] Bidirectional inter-prediction 600 is similar to unidirectional inter-prediction 500, but employs a pair of reference frames to predict a current block 611 in a current frame 610. Hence current frame 610 and current block 611 are substantially similar to current frame 510 and current block 511, respectively. The current frame 610 is temporally positioned between a preceding reference frame 620, which occurs before the current frame 610 in the video sequence, and a subsequent reference frame 630, which occurs after the current frame 610 in the video sequence. Preceding reference frame 620 and subsequent reference frame 630 are otherwise substantially similar to reference frame 530.

[00143] The current block 611 is matched to a preceding reference block 621 in the preceding reference frame 620 and to a subsequent reference block 631 in the subsequent reference frame 630. Such a match indicates that, over the course of the video sequence, an object moves from a position at the preceding reference block 621 to a position at the subsequent reference block 631 along a motion trajectory 613 and via the current block 611. The current frame 610 is separated from the preceding reference frame 620 by some preceding temporal distance (TD0) 623 and separated from the subsequent reference frame 630 by some subsequent temporal distance (TD1) 633. The TD0 623 indicates an amount of time between the preceding reference frame 620 and the current frame 610 in the video sequence in units of frames. The TD1 633 indicates an amount of time between the current frame 610 and the subsequent reference frame 630 in the video sequence in units of frame. Hence, the object moves from the preceding reference block 621 to the current block 611 along the motion trajectory 613 over a time period indicated by TD0 623. The object also moves from the current block 611 to the subsequent reference block 631 along the motion trajectory 613 over a time period indicated by TDl 633. The prediction information for the current block 611 may reference the preceding reference frame 620 and/or preceding reference block 621 and the subsequent reference frame 630 and/or subsequent reference block 631 by a pair of reference indices indicating the direction and temporal distance between the frames.

[00144] A preceding motion vector (MV0) 625 describes the direction and magnitude of the movement of the object along the motion trajectory 613 over the TD0 623 (e.g., between the preceding reference frame 620 and the current frame 610). A subsequent motion vector (MV1) 635 describes the direction and magnitude of the movement of the object along the motion trajectory 613 over the TDl 633 (e.g., between the current frame 610 and the subsequent reference frame 630). As such, in bidirectional inter-prediction 600, the current block 611 can be coded and reconstructed by employing the preceding reference block 621 and/or the subsequent reference block 631, MV0 625, and MV1 635.

[00145] In both merge mode and AMVP mode, a candidate list is generated by adding candidate motion vectors to a candidate list in an order defined by a candidate list determination pattern. Such candidate motion vectors may include motion vectors according to unidirectional inter-prediction 500, bidirectional inter-prediction 600, or combinations thereof. Specifically, motion vectors are generated for neighboring blocks when such blocks are encoded. Hence, the candidate motion vectors include motion vectors generated according to unidirectional inter-prediction 500 or bidirectional inter-prediction 600, depending on which approach is used when such neighboring blocks are encoded. Examples of candidate list determination patterns and corresponding available coded block positions employed to select the candidate list determination patterns are disclosed with respect to the FIGS. 7- 17 below.

[00146] FIG. 7 is a schematic diagram illustrating a first example available coded block position 700. An encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can employ the available coded block position 700 to select a candidate list determination pattern for use in generating a candidate list. Such a candidate list can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00147] The available coded block position 700 includes a current block 701 and coded blocks 702. The current block 701 is a block being encoded at an encoder or decoded at a decoder, depending on the example, at a specified time. The coded blocks 702 are blocks that are already encoded at the specified time. Hence, the coded blocks 702 are potentially available for use when generating a candidate list. The current block 701 and the coded blocks 702 are included in a common frame. Further, the coded blocks 702 each contain a boundary that is immediately adjacent to (e.g., abuts) a boundary of the current block 701. In available coded block position 700, the available coded blocks 702 are positioned above the current block 701 and left of the current block 701.

[00148] FIG. 8 is a schematic diagram illustrating an example candidate list determination pattern 800 selected based on the first example available coded block position 700. Specifically, an encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can select the candidate list determination pattern 800 for use in generating a candidate list when the available coded block position 700 is present relative to a current block 801. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter-prediction according to unidirectional inter- prediction 500 and/or bidirectional inter-prediction 600.

[00149] The candidate list determination pattern 800 searches positions Ao 860, Ai 861, Bo 870, Bi 871, and/or B2 872 for valid candidate motion vectors. Such candidate motion vectors can then be positioned in a candidate list in a predetermined checking order. The candidate list can then be employed to select a motion vector to perform inter-prediction for the current block 801. In candidate list determination pattern 800, position Ao 860 abuts the bottom left corner of the current block 801. Position Ai 861 abuts the left side of the current block 801, and contains a lower border that abuts an upper border of position Ao 860. Further, position Bo 870 abuts the top right corner of the current block 801. Position Bi 871 abuts the top side of the current block 801, and contains a right border that abuts a left border of position Bo 870. Also, position B2 872 abuts the top left corner of the current block 801.

[00150] As the candidate list determination pattern 800 is selected when the available coded block position 700 occurs, coded blocks are positioned above and to the left of the current block 801. Hence positions A ₀ 860, A _! 861, B ₀ 870, B _! 871, and B ₂ 872 are each likely to be associated with a coded block, such as coded blocks 702. As such, positions Ao 860, Ai 861, Bo 870, Bi 871, and B2 872 are likely to be associated with previously coded motion vectors that can be included in a candidate list. Accordingly, the candidate list determination pattern 800 can be employed to search available coded blocks adjacent to a bottom left corner, a top right corner, and a top left corner of the current block 801 when the available coded blocks are positioned above the current block 801 and left of the current block 801.

[00151] As noted above, the candidate list determination pattern 800 can be employed for both unidirectional inter-prediction and/or bidirectional inter-prediction. In unidirectional inter- prediction, the motion vectors point to blocks in a preceding reference frame or a subsequent reference frame. These frames are considered list 0 (preceding) or list 1 (subsequent) pictures. Bidirectional inter-prediction references both list 0 and list 1. The current block 801 is encoded according to list 0, list 1, or both. Hence, the coded blocks are also encoded according to list 0, list 1, or both. When the candidate list is generated, the reference index of the motion vectors at positions Ao 860, Ai 861, Bo 870, Bi 871, and B2 872 may be scaled in order to reference the same list as the current block 801.

[00152] In some cases, additional positions can be considered for addition to the motion vector candidate list. For example, blocks positioned temporally adjacent to the current block 801 can also be considered. In this context, temporally adjacent indicates a block in a preceding frame or a subsequent frame. Specifically, a temporal bottom right collocated candidate (TBR) position and a temporal central collocated candidate (TCT) position can be considered. The TBR position abuts the bottom right corner of the current block 801 in a temporally adjacent frame. The TCT position is positioned at the position of the current block 801 in a temporally adjacent frame. Hence, motion vectors from the TCT position and the TBR position can be added to the candidate list. A zero motion vector can also be considered for addition to the motion vector candidate list. The zero motion vector indicates the reference block is in the same position as the current block 801 in a temporally adjacent frame.

[00153] The candidate list can be constrained by a maximum candidate list number. This prevents generation of an overly large candidate list when many valid candidate motion vectors exist. An overly large candidate list would necessitate employing a large candidate index to indicate the selected motion vector candidate. The large candidate index would in turn increase the encoding size. Then a maximum candidate list number can be signaled in the bitstream, for example as a sequence level parameter set (SPS) parameter and/or a picture level parameter set (PPS) parameter.

[00154] The candidate list can be generated based on the positions/vectors discussed above in a predefined checking order as constrained by the maximum candidate list number. Hence, the candidate list determination pattern 800 searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. Valid candidate motion vectors are added to the candidate list until the maximum candidate list number is reached. Duplicate motion vectors may also be pruned from the candidate list to allow for more unique candidates that the encoder can choose from. Many example predefined checking orders can be employed.

[00155] In a first example, the predefined checking order includes checking blocks in A positions (Ao 860, Ai 861) with a common reference index with the current block, then checking blocks in an A positions with a scaled reference index (e.g., scaled due to referencing different picture list), then checking blocks in B positions (Bo 870, Bi 871, and B ₂ 872) with a common reference index with the current block, then checking blocks in a B position with a scaled reference index, and then checking TBR, TCT, and zero MV. A most frequently used motion vector can also be inserted at the end of the predefined checking order in some examples.

[00156] In a second example, the predefined checking order includes checking blocks in a B position (B ₀ 870, Bi 871, and B ₂ 872) with a common reference index with the current block, then checking blocks in a B position with a scaled reference index, then checking blocks in an A position (Ao 860, Ai 861) with a common reference index with the current block, then checking blocks in an A position with a scaled reference index, and then checking TBR, TCT, and zero MV. A most frequently used motion vector can also be inserted at the end of the predefined checking order in some examples.

[00157] In a third example, the predefined checking order includes checking blocks in a B position (Bo 870, Bi 871, and B ₂ 872) with a common reference index with the current block, then checking blocks in an A position (Ao 860, Ai 861) with a common reference index with the current block, then checking blocks in a B position with a scaled reference index, then checking blocks in an A position with a scaled reference index, and then checking TBR, TCT, and zero MV. A most frequently used motion vector can also be inserted at the end of the predefined checking order in some examples.

[00158] In a fourth example, the predefined checking order includes checking blocks in a B position (B ₀ 870, Bi 871, and B ₂ 872) with a common reference index with the current block, then checking blocks in an A position (Ao 860, Ai 861) with a common reference index with the current block, then checking blocks in an A position with a scaled reference index, then checking blocks in a B position with a scaled reference index, and then checking TBR, TCT, and zero MV. A most frequently used motion vector can also be inserted at the end of the predefined checking order in some examples.

[00159] In a fifth example, the predefined checking order includes checking blocks in an A position (Ao 860, Ai 861) with a common reference index with the current block, then checking blocks in a B position (Bo 870, Bi 871, and B ₂ 872) with a common reference index with the current block, then checking blocks in a B position with a scaled reference index, then checking blocks in an A position with a scaled reference index, and then checking TBR, TCT, and zero MV. A most frequently used motion vector can also be inserted at the end of the predefined checking order in some examples. [00160] In a six example, the predefined checking order includes checking blocks in an A position (Ao 860, Ai 861) with a common reference index with the current block, then checking blocks in a B position (Bo 870, Bi 871, and B2 872) with a common reference index with the current block, then checking blocks in an A position with a scaled reference index, then checking blocks in a B position with a scaled reference index, and then checking TBR, TCT, and zero MV. A most frequently used motion vector can also be inserted at the end of the predefined checking order in some examples.

[00161] FIG. 9 is a schematic diagram illustrating a second example available coded block position 900. An encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can employ the available coded block position 900 to select a candidate list determination pattern for use in generating a candidate list. Such a candidate list can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600. The available coded block position 900 includes a current block 901 and coded blocks 902, which are similar to current block 701 and coded blocks 702, respectively. In available coded block position 900, the available coded blocks 902 are positioned above the current block 901 and right of the current block 901.

[00162] FIG. 10 is a schematic diagram illustrating an example candidate list determination pattern 1000 selected based on the second example available coded block position 900. Specifically, an encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can select the candidate list determination pattern 1000 for use in generating a candidate list when the available coded block position 900 is present relative to a current block 1001. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00163] The candidate list determination pattern 1000 searches positions A ₀ 1060, Ai 1061, Bo 1070, Bi 1071, and/or B2 1072 for valid candidate motion vectors. Such candidate motion vectors can then be positioned in a candidate list in a predetermined checking order. The candidate list can then be employed to select a motion vector to perform inter-prediction for the current block 1001. In candidate list determination pattern 1000, position Ao 1060 abuts the bottom right corner of the current block 1001. Position Ai 1061 abuts the right side of the current block 1001, and contains a lower border that abuts an upper border of position Ao 1060. Further, position Bo 1070 abuts the top left corner of the current block 1001. Position Bi 1071 abuts the top side of the current block 1001, and contains a left border that abuts a right border of position Bo 1070. Also, position B2 1072 abuts the top right corner of the current block 1001.

[00164] As the candidate list determination pattern 1000 is selected when the available coded block position 900 occurs, coded blocks are positioned above and to the right of the current block 1001. Hence positions A ₀ 1060, Ai 1061, B ₀ 1070, Bi 1071, and B ₂ 1072 are each likely to be associated with a coded block, such as coded blocks 902. As such, positions A ₀ 1060, A _! 1061, B ₀ 1070, B _{ 1071, and B ₂ 1072 are likely to be associated with previously coded motion vectors that can be included in a candidate list. Accordingly, the candidate list determination pattern 1000 can be employed to search available coded blocks adjacent to a bottom right corner, a top left corner, and a top right corner of the current block 1001 when the available coded blocks are positioned above the current block 1001 and right of the current block 1001.

[00165] As noted above, discussed with respect to FIG. 8, the candidate list determination pattern 1000 can be employed for both unidirectional inter-prediction and/or bidirectional inter- prediction. Hence, the reference index of the motion vectors at positions Ao 1060, Ai 1061, Bo 1070, Bi 1071, and B ₂ 1072 may be scaled in order to reference the same list as the current block 1001. Further, TBR position and TCT position can be considered for addition to the candidate list. Also, a most frequently used vector and/or a zero motion vector can be considered for addition to the motion vector candidate list.

[00166] The candidate list can be generated based on the positions/vectors discussed above in a predefined checking order as constrained by a maximum candidate list number. Hence, the candidate list determination pattern 1000 searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. Valid candidate motion vectors are added to the candidate list until the maximum candidate list number is reached. Duplicate motion vectors may also be pruned from the candidate list to allow for more unique candidates that the encoder can choose from. Many example predefined checking orders can be employed, such as any of the predefined checking orders discussed with respect to FIG. 8.

[00167] FIG. 11 is a schematic diagram illustrating a third example available coded block position 1100. An encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can employ the available coded block position 1100 to select a candidate list determination pattern for use in generating a candidate list. Such a candidate list can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600. The available coded block position 1100 includes a current block 1101 and coded blocks 1102, which are similar to current block 701 and coded blocks 702, respectively. In available coded block position 1100, the available coded blocks 1102 are positioned above the current block 1101 and below the current block 1101.

[00168] FIG. 12 is a schematic diagram illustrating an example candidate list determination pattern 1200 selected based on the third example available coded block position 1100. Specifically, an encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can select the candidate list determination pattern 1200 for use in generating a candidate list when the available coded block position 1 100 is present relative to a current block 1201. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00169] The candidate list determination pattern 1200 searches positions Ao 1260, Ai 1261, A ₂ 1262, A ₃ 1263, B ₀ 1270, Bi 1271, B ₂ 1272, and/or B ₃ 1273 for valid candidate motion vectors. Such candidate motion vectors can then be positioned in a candidate list in a predetermined checking order. The candidate list can then be employed to select a motion vector to perform inter-prediction for the current block 1201. In candidate list determination pattern 1200, position Ao 1260 abuts the bottom left corner of the current block 1201. Position Ai 1261 abuts the bottom side of the current block 1201, and contains a left border that abuts a right border of position Ao 1260. Position A3 1263 abuts the bottom right corner of the current block 1201. Position A ₂ 1062 abuts the bottom side of the current block 1201, and contains a right border that abuts a left border of position A3 1263. Further, position Bo 1270 abuts the top left corner of the current block 1201. Position Bi 1271 abuts the top side of the current block 1201, and contains a left border that abuts a right border of position Bo 1270. Position B ₃ 1273 abuts the top right corner of the current block 1201. Position B ₂ 1272 abuts the top side of the current block 1201, and contains a right border that abuts a left border of position B ₃ 1273.

[00170] As the candidate list determination pattern 1200 is selected when the available coded block position 1100 occurs, coded blocks are positioned above and below the current block 1201. Hence positions A ₀ 1260, Ai 1261, A ₂ 1262, A ₃ 1263, B ₀ 1270, Bi 1271, B ₂ 1272, and B ₃ 1273 are each likely to be associated with a coded block, such as coded blocks 1 102. As such, positions A ₀ 1260, Ai 1261, A ₂ 1262, A ₃ 1263, B ₀ 1270, Bi 1271, B ₂ 1272, and B ₃ 1273 are likely to be associated with previously coded motion vectors that can be included in a candidate list. Accordingly, the candidate list determination pattern 1200 can be employed to search available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block 1201 when the available coded blocks are positioned above the current block 1201 and below the current block 1201.

[00171] As noted above, discussed with respect to FIG. 8, the candidate list determination pattern 1200 can be employed for both unidirectional inter-prediction and/or bidirectional inter- prediction. Hence, the reference index of the motion vectors at positions Ao 1260, Ai 1261, A2 1262, A3 1263, Bo 1270, Bi 1271, B2 1272, and B3 1273 may be scaled in order to reference the same list as the current block 1201. Further, TBR position and TCT position can be considered for addition to the candidate list. Also, a most frequently used vector and/or a zero motion vector can be considered for addition to the motion vector candidate list.

[00172] The candidate list can be generated based on the positions/vectors discussed above in a predefined checking order as constrained by a maximum candidate list number. Hence, the candidate list determination pattern 1200 searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. Valid candidate motion vectors are added to the candidate list until the maximum candidate list number is reached. Duplicate motion vectors may also be pruned from the candidate list to allow for more unique candidates that the encoder can choose from. Many example predefined checking orders can be employed, such as any of the predefined checking orders discussed with respect to FIG. 8.

[00173] FIG. 13 is a schematic diagram illustrating a fourth example available coded block position 1300. An encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can employ the available coded block position 1300 to select a candidate list determination pattern for use in generating a candidate list. Such a candidate list can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600. The available coded block position 1300 includes a current block 1301 and coded blocks 1302, which are similar to current block 701 and coded blocks 702, respectively. In available coded block position 1300, the available coded blocks 1302 are positioned above the current block 1301, right of the current block 1301, and left of the current block 1301.

[00174] FIG. 14 is a schematic diagram illustrating an example candidate list determination pattern 1400 selected based on the fourth example available coded block position 1300. Specifically, an encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can select the candidate list determination pattern 1400 for use in generating a candidate list when the available coded block position 1300 is present relative to a current block 1401. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00175] The candidate list determination pattern 1400 searches positions Ao 1460, Ai 1461, A ₂ 1462, A ₃ 1463, B ₀ 1470, Bi 1471, B ₂ 1472, and/or B ₃ 1473 for valid candidate motion vectors. Such candidate motion vectors can then be positioned in a candidate list in a predetermined checking order. The candidate list can then be employed to select a motion vector to perform inter-prediction for the current block 1401. In candidate list determination pattern 1400, position A ₀ 1460 abuts the bottom left corner of the current block 1401. Position Ai 1461 abuts the left side of the current block 1401, and contains a bottom border that abuts a top border of position Ao 1460. Position A ₂ 1462 abuts the bottom right corner of the current block 1401. Position A3 1463 abuts the right side of the current block 1401, and contains a bottom border that abuts a top border of position A ₂ 1462. Further, position Bo 1470 abuts the top left corner of the current block 1401. Position Bi 1471 abuts the top side of the current block 1401, and contains a left border that abuts a right border of position Bo 1470. Position B ₃ 1473 abuts the top right corner of the current block 1401. Position B ₂ 1472 abuts the top side of the current block 1401, and contains a right border that abuts a left border of position B ₃ 1473.

[00176] As the candidate list determination pattern 1400 is selected when the available coded block position 1300 occurs, coded blocks are positioned above, left, and right of the current block 1401. Hence positions A ₀ 1460, Ai 1461, A ₂ 1462, A ₃ 1463, B ₀ 1470, Bi 1471, B ₂ 1472, and/or B ₃ 1473 are each likely to be associated with a coded block, such as coded blocks 1302. As such, positions A ₀ 1460, Ai 1461, A ₂ 1462, A ₃ 1463, B ₀ 1470, Bi 1471, B ₂ 1472, and/or B ₃ 1473 are likely to be associated with previously coded motion vectors that can be included in a candidate list. Accordingly, the candidate list determination pattern 1400 can be employed to search available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block 1401 when the available coded blocks are positioned above the current block 1401, left of the current block 1401, and right of the current block 1401.

[00177] As noted above, discussed with respect to FIG. 8, the candidate list determination pattern 1400 can be employed for both unidirectional inter-prediction and/or bidirectional inter- prediction. Hence, the reference index of the motion vectors at positions Ao 1460, Ai 1461, A ₂ 1462, A ₃ 1463, B ₀ 1470, Bi 1471, B ₂ 1472, and/or B ₃ 1473 may be scaled in order to reference the same list as the current block 1401. Further, TBR position and TCT position can be considered for addition to the candidate list. Also, a most frequently used vector and/or a zero motion vector can be considered for addition to the motion vector candidate list. [00178] The candidate list can be generated based on the positions/vectors discussed above in a predefined checking order as constrained by a maximum candidate list number. Hence, the candidate list determination pattern 1400 searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. Valid candidate motion vectors are added to the candidate list until the maximum candidate list number is reached. Duplicate motion vectors may also be pruned from the candidate list to allow for more unique candidates that the encoder can choose from. Many example predefined checking orders can be employed, such as any of the predefined checking orders discussed with respect to FIG. 8.

[00179] FIG. 15 is a schematic diagram illustrating another example candidate list determination pattern 1500 selected based on the fourth example available coded block position 1300. Specifically, an encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can select the candidate list determination pattern 1500 for use in generating a candidate list when the available coded block position 1300 is present relative to a current block 1501. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00180] The candidate list determination pattern 1500 searches positions Ao 1560, Ai 1561, Bo 1570, Bi 1571, B2 1572, and/or B3 1573 for valid candidate motion vectors. Positions Bo 1570, B i 1571, B ₂ 1572, and/or B ₃ 1573 are substantially similar to positions B ₀ 1470, Bi 1471, B2 1472, and/or B3 1473, respectively. Position Ao 1560 abuts the left side of the current block 1501 and is adjacent to the bottom left corner of the current block 1501. Position Ai 1561 abuts the right side of the current block 1501 and is adjacent to the bottom right corner of the current block 1501. Candidate list determination pattern 1500 is substantially similar to candidate list determination pattern 1400, but omits positions below the current block 1501. For example, candidate list determination pattern 1500 can be employed when the current block 1501 is positioned as the bottom block of a frame, and hence no valid below the current block 1501 exist.

[00181] FIG. 16 is a schematic diagram illustrating a fifth example available coded block position 1600. An encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can employ the available coded block position 1600 to select a candidate list determination pattern for use in generating a candidate list. Such a candidate list can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600. The available coded block position 1600 includes a current block 1601 and coded blocks 1602, which are similar to current block 701 and coded blocks 702, respectively. In available coded block position 1600, the available coded blocks 1602 are positioned above the current block 1601, below the current block 1601, left of the current block 1601, and right of the current block 1601.

[00182] FIG. 17 is a schematic diagram illustrating an example candidate list determination pattern 1700 selected based on the fifth example available coded block position 1600. Specifically, an encoder 300 and/or a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can select the candidate list determination pattern 1700 for use in generating a candidate list when the available coded block position 1600 is present relative to a current block 1701. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter-prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00183] The candidate list determination pattern 1700 searches positions Ao 1760, Ai 1761, A ₂ 1762, A ₃ 1763, A ₄ 1764, A ₅ 1765, B ₀ 1770, Bi 1771, B ₂ 1772, B ₃ 1773, B ₄ 1774, and/or B ₅ 1775 for valid candidate motion vectors. Such candidate motion vectors can then be positioned in a candidate list in a predetermined checking order. The candidate list can then be employed to select a motion vector to perform inter-prediction for the current block 1701. In candidate list determination pattern 1700, position Ao 1760 abuts the bottom left corner of the current block 1701. Position Ai 1761 abuts the left side of the current block 1701, and contains a bottom border that abuts a top border of position Ao 1760. Position A ₂ 1761 abuts the bottom side of the current block 1701, and contains a left border that abuts a right border of position Ao 1760. Position A ₃ 1763 abuts the bottom right corner of the current block 1701. Position A ₄ 1764 abuts the bottom side of the current block 1701, and contains a right border that abuts a left border of position A ₃ 1762. Position A5 1765 abuts the right side of the current block 1701, and contains a bottom border that abuts a top border of position A ₃ 1762. Further, position B ₀ 1770 abuts the top left corner of the current block 1701. Position Bi 1771 abuts the top side of the current block 1701, and contains a left border that abuts a right border of position Bo 1770. Position B ₂ 1772 abuts the left side of the current block 1701, and contains a top border that abuts a bottom border of position Bo 1770. Position B ₃ 1773 abuts the top right corner of the current block 1701. Position B ₄ 1774 abuts the top side of the current block 1701, and contains a right border that abuts a left border of position B ₃ 1773. Position B ₃ 1773 abuts the top right corner of the current block 1701. Position B5 1775 abuts the right side of the current block 1701, and contains a top border that abuts a bottom border of position B ₃ 1773. [00184] As the candidate list determination pattern 1700 is selected when the available coded block position 1600 occurs, coded blocks are positioned above, below, left, and right of the current block 1701. Hence positions A ₀ 1760, Ai 1761, A ₂ 1762, A ₃ 1763, A4 1764, A ₅ 1765, Bo 1770, Bi 1771, B ₂ 1772, B ₃ 1773, B ₄ 1774, and/or B ₅ 1775 are each likely to be associated with a coded block, such as coded blocks 1602. As such, positions Ao 1760, Ai

1761, A ₂ 1762, A ₃ 1763, A4 1764, A ₅ 1765, B ₀ 1770, Bi 1771, B ₂ 1772, B ₃ 1773, B ₄ 1774, and/or B ₅ 1775 are likely to be associated with previously coded motion vectors that can be included in a candidate list. Accordingly, the candidate list determination pattern 1700 can be employed to search available coded blocks adjacent to a bottom left corner, a bottom right corner, a top left corner, and a top right corner of the current block 1701 when the available coded blocks are positioned above the current block 1701, below the current block 1701, left of the current block 1701, and right of the current block 1701.

[00185] As noted above, discussed with respect to FIG. 8, the candidate list determination pattern 1700 can be employed for both unidirectional inter-prediction and/or bidirectional inter- prediction. Hence, the reference index of the motion vectors at positions Ao 1760, Ai 1761, A ₂

1762, A ₃ 1763, A4 1764, A ₅ 1765, B ₀ 1770, Bi 1771, B ₂ 1772, B ₃ 1773, B ₄ 1774, and/or B ₅ 1775 may be scaled in order to reference the same list as the current block 1701. Further, TBR position and TCT position can be considered for addition to the candidate list. Also, a most frequently used vector and/or a zero motion vector can be considered for addition to the motion vector candidate list.

[00186] The candidate list can be generated based on the positions/vectors discussed above in a predefined checking order as constrained by a maximum candidate list number. Hence, the candidate list determination pattern 1700 searches available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. Valid candidate motion vectors are added to the candidate list until the maximum candidate list number is reached. Duplicate motion vectors may also be pruned from the candidate list to allow for more unique candidates that the encoder can choose from. Many example predefined checking orders can be employed, such as any of the predefined checking orders discussed with respect to FIG. 8.

[00187] FIG. 18 is a flowchart of an example method 1800 of selecting a candidate list determination pattern based on available coded block position at an encoder. Specifically, an encoder 300 operating method 100 and/or employing the functionality of codec system 200 can employ method 1800 to select the candidate list determination pattern for use in generating a candidate list. Method 1800 may select candidate list determination patterns 800, 1000, 1200, 1400, 1500, and/or 1700 based on available coded block positions 700, 900, 1100, 1300, and/or 1600 as discussed above with respect to corresponding figures. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter- prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00188] Method 1800 is initiated when an encoder determines to perform inter-prediction for a current block, for example in AMVP or merge mode. At step 1801, the encoder selects a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block. At step 1803, the encoder applies the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block. The selected candidate list determination pattern can search the available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. For example, checking orders as discussed with respect to FIG. 8 can be employed. At step 1805, the encoder selects a selected motion vector from the candidate list to encode the current block. At step 1807, the encoder encodes a candidate index corresponding to the selected motion vector in a bitstream. The candidate index and a reference index provide sufficient information to reconstruct the current block at a decoder. The reference index may be encoded in the bitstream as data and/or defined according to syntax. In the AMVP case, the encoder may also encode a difference between a selected motion vector for the current block and a selected candidate motion vector in the candidate list. At step 1809, the encoder transmits the bitstream to support reconstruction of the current block for display at a video decoder.

[00189] FIG. 19 is a flowchart of an example method 1900 of selecting a candidate list determination pattern based on available coded block position at a decoder. Specifically, a decoder 400 operating method 100 and/or employing the functionality of codec system 200 can employ method 1900 to select the candidate list determination pattern for use in generating a candidate list. Method 1900 may select candidate list determination patterns 800, 1000, 1200, 1400, 1500, and/or 1700 based on available coded block positions 700, 900, 1100, 1300, and/or 1600 as discussed above with respect to corresponding figures. The resulting candidate list may be a merge candidate list or an AMVP candidate list, which can be employed in inter- prediction according to unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600.

[00190] Method 1900 is initiated when a decoder determines to perform inter-prediction for a current block, for example in AMVP or merge mode, based on information in a bitstream. At step 1901, the decoder receives a candidate list index in a bitstream. At step 1903, the decoder selects a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block. At step 1905, the decoder can apply the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block. The selected candidate list determination pattern can search the available coded blocks for motion vector candidates in a predefined checking order based on available coded block position. For example, checking orders as discussed with respect to FIG. 8 can be employed. At step 1907, the decoder applies the candidate list index from the bitstream to the candidate list of motion vectors to determine a motion vector for the current block. At step 1909, the decoder reconstructs the current block for display based on the motion vector. In the AMVP case, the motion vector is determined based on the candidate motion vector from the candidate list and a difference between the candidate motion vector and the selected motion vector. Reconstructing the current block includes obtaining a reference block based on a reference index and the motion vector. The reference block is combined with any residual data to reconstruct the current block. The current block is positioned in a frame with other blocks. The frame is positioned in a video sequence, which is displayed to a user via a display.

[00191] FIG. 20 is a schematic diagram of an example video coding device 2000 according to an embodiment of the disclosure. The video coding device 2000 is suitable for implementing the disclosed examples/embodiments as described herein. The video coding device 2000 comprises downstream ports 2020, upstream ports 2050, and/or transceiver units (Tx/Rx) 2010, including transmitters and/or receivers for communicating data upstream and/or downstream over a network. The video coding device 2000 also includes a processor 2030 including a logic unit and/or central processing unit (CPU) to process the data and a memory 2032 for storing the data. The video coding device 2000 may also comprise optical-to-electrical (OE) components, electrical-to-optical (EO) components, and/or wireless communication components coupled to the upstream ports 2050 and/or downstream ports 2020 for communication of data via optical or wireless communication networks. The video coding device 2000 may also include input and/or output (I/O) devices 2060 for communicating data to and from a user. The I/O devices 2060 may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. The I/O devices 2060 may also include input devices, such as a keyboard, mouse, trackball, etc., and/or corresponding interfaces for interacting with such output devices. [00192] The processor 2030 is implemented by hardware and software. The processor 2030 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors (DSPs). The processor 2030 is in communication with the downstream ports 2020, Tx/Rx 2010, upstream ports 2050, and memory 2032. The processor 2030 comprises a coding module 2014. The coding module 2014 implements the disclosed embodiments described above, such as methods 100, 1800, and/or 1900, unidirectional inter-prediction 500, bidirectional inter-prediction 600, and/or any other method/mechanism described herein. Further, the coding module 2014 may implement a codec system 200, an encoder 300, and/or a decoder 400. For example, coding module 2014 can be employed to generate a candidate list as either an encoder or decoder. Specifically, the coding module 2014 may select a candidate list determination pattern 800, 1000, 1200, 1400, 1500, and/or 1700 based on available coded block positions 700, 900, 1100, 1300, and/or 1600. The coding module 2014 can then employ the selected candidate list determination pattern in a predefined checking order to generate the candidate list. As an encoder, the coding module 2014 can determine a motion vector for a current block based on the candidate list, and encode the current block as a candidate index. As a decoder, the coding module 2014 can determine a motion vector for a current block based on the candidate list and a candidate index received in a bitstream. Further, coding module 2014 effects a transformation of the video coding device 2000 to a different state. Alternatively, the coding module 2014 can be implemented as instructions stored in the memory 2032 and executed by the processor 2030 (e.g., as a computer program product stored on a non-transitory medium).

[00193] The memory 2032 comprises one or more memory types such as disks, tape drives, solid-state drives, read only memory (ROM), random access memory (RAM), flash memory, ternary content-addressable memory (TCAM), static random-access memory (SRAM), etc. The memory 2032 may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution.

[00194] FIG. 21 is a schematic diagram 2100 of example devices for selecting a candidate list determination pattern based on available coded block position. The schematic diagram 2100 includes a video encoder 2102 and a video decoder 2110, which can implement operating method 100, method 1800, codec system 200, encoder 300, and/or a decoder 400. Further, the video encoder 2102 and video decoder 2110 can perform unidirectional inter-prediction 500 and/or bidirectional inter-prediction 600 by selecting a candidate list determination pattern 800, 1000, 1200, 1400, 1500, and/or 1700 based on available coded block positions 700, 900, 1100, 1300, and/or 1600.

[00195] The video encoder 2102 includes a pattern selection module 2101 for selecting a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block. The video encoder 2102 also includes a candidate list generation module 2103 for applying the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block. The video encoder 2102 also includes a motion vector selection module 2105 for selecting a selected motion vector from the candidate list to encode the current block. The video encoder 2102 also includes an encoding module 2107 for encoding a candidate index corresponding to the selected motion vector in a bitstream. The video encoder 2102 also includes a transmitter 2109 for transmitting the bitstream to support reconstruction of the current block for display at a video decoder 2110.

[00196] The video decoder 21 10 includes a receiver 21 17 for receiving a candidate list index in a bitstream. The video decoder 2110 also includes a pattern selection module 21 11 for selecting a selected candidate list determination pattern from a plurality of candidate list determination patterns based on available coded blocks around a current block. The video decoder 2110 also includes a candidate list generation module 21 13 for applying the selected candidate list determination pattern to the available coded blocks to generate a candidate list of motion vectors for the current block. The video decoder 2110 also includes a motion vector determination module 21 15 for determining a motion vector for the current block based on the candidate list of motion vectors and the candidate list index. The video decoder 2110 also includes a reconstruction module 2119 for reconstructing the current block for display via a display device based on the motion vector.

[00197] A first component is directly coupled to a second component when there are no intervening components, except for a line, a trace, or another medium between the first component and the second component. The first component is indirectly coupled to the second component when there are intervening components other than a line, a trace, or another medium between the first component and the second component. The term "coupled" and its variants include both directly coupled and indirectly coupled. The use of the term "about" means a range including ±10% of the subsequent number unless otherwise stated.

[00198] While several embodiments have been provided in the present disclosure, it may be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

[00199] In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, components, techniques, or methods without departing from the scope of the present disclosure. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and may be made without departing from the spirit and scope disclosed herein.