CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority to U.S. Provisional Patent Application No. 60/582,296 filed June 23, 2004 entitled "Synchronization Check System For Film Projectors" the entirety of which is hereby incorporated in its entirely by this reference. FIELD OF THE INVENTION [0002] The field of the invention relates to projection systems, and specifically to projection systems with the ability to check the synchronization of an audio track with the images of a motion picture as it is being presented. BACKGROUND [0003] The history of synchronizing a sound track with a series of motion picture images began in 1926-1927 when sound was first introduced to motion pictures. An early innovation was the Warner Bros. Vitaphone, a sound-on-disc, or phonograph approach that was mechanically synchronized to the film projector. An alternate approach to sound synchronization appeared a few years later and involved optically recording an analog sound track on the edge of the motion picture film. An advantage of this latter approach was that synchronization was more robust and reliable, and this method remains in use today. A disadvantage of the soundtrack on film approach however is that it typically occupies space within the image area which reduces the amount of visual information that can be projected on the screen. A further consequence with the use of image area to record sound information is that the image aspect ratio is changed. The motion picture industry adopted the Academy Aperture standard to restore the aspect ratio of 35mm film back to a 1.33 ratio, which it was before the addition of optical sound tracks reduced it to 1.15: 1 (although the size of the picture area was further reduced). A further disadvantage of recording optical sound tracks on the edge of film is that the amount of space to write information is necessarily limited thereby limiting the amount of audio information written on the film. This limitation on the amount of audio information placed an effective cap on the possible quality of soundtracks encoded on the edge of film. Another sound-on-film method which appeared was placing a magnetic sound track on the edge of the film which was synchronized to the images of the motion picture by its' relative position on the fϊlmstrip. [0004] In the 1990s motion picture , studios and technology companies began using digitally encoded sound tracks on film in an attempt to improve the sound quality of motion pictures. In 1990 Eastman Kodak and the Optical Radiation Corporation released Cinema Digital Sound (CDS) which was a six channel digital soundtrack optically recorded on the filmstrip in place of the traditional analog soundtrack. Although it provided better quality it required motion picture exhibitors to purchase expensive decoding equipment. Dolby Stereo Digital (SR-D), which debuted in 1991, was another six channel digital system, which was recorded optically on the filmstrip but in the area between sprocket holes, thereby allowing the presence of the traditional analog soundtrack as a backup in case of a failure with the higher quality digital soundtrack. A disadvantage of the SD-R system was that the digital information was recorded on the filmstrip in a position that typically sees a significant amount of mechanical wear and was thus vulnerable to physical deterioration over time. [0005] Digital Theatre Systems (DTS) which first appeared in 1993 on the film Jurassic Park was yet another digital sound system, but differed from CDS and SR-D in that an optical time code or indexing track was recorded onto the filmstrip which then was then used to synchronize six channels of sound stored on separate CD-ROM discs. Like SR-D, DTS time code is not recorded overtop the analog sound track and so it remains in place as a potential backup in case of failure. A disadvantage of DTS is that it involves a separate processing step in the production of motion picture film prints and requires the use of proprietary decoding equipment. [0006] Sony Dynamic Digital Sound (SDSS) is another digital sound system that first appeared in 1993 and features 6 to 8 digital soundtracks recorded on both edges of the film outside of the perforation area. Like DTS and SR-D, SDSS is compatible with an analog sound track written on the film in the traditional area. [0007] The applicant, Imax Corporation, also standardized on a digital sound system in the 1980s to improve on the analog system it had been using since 1970, which was based on synchronizing the film strip with a separate magnetic reel to reel sound track with an electro¬ mechanical shaft encoder. The system required the manual positioning of an index film frame relative to the shaft encoder, which subsequently recorded the passage of film frames to generate time code data to keep the magnetic tape player in synchronization with the projector. [0008] The digital sound system introduced by Imax/Sonics in the 1980s, the Digital Disc Player (DDP) discussed in U.S. Patent Nos. 5,132,955 and 5,226,046, replaced the magnetic tape drive with a set of three Compact Discs, each one containing two soundtracks for a total of six. The method of synchronizing the sound tracks with images on the screen was essentially the same as before; manual initiation of initial synchronization that was maintained by bi-phase signals produced by a shaft encoder on a film sprocket. Subsequent Imax/Sonics sound systems such as the DTAC and DFPIl use digital sound tracks stored on a computer hard drive. [0009] U.S. Patents Nos. 5,751,398, 5,386,255, and 5,155,510 assigned to Digital Theatre Systems describe some of the patentable features of the DTS System. All of the above patents discuss a system that features the use of a digital time code encoded optically on the side of the film to provide synchronization between the images and a digital sound track stored separately from the motion picture film. U.S. Patent No. 5,386,255 makes reference to synchronizing the readout of digital audio data from a FIFO (first in first out) to the alternating current (AC) supplied to the motion picture projector. This allows the system to continue operation in the case of missing time code data and ensures a positive synchronization between the film advance and sound readout rates. The digital audio data is supplied to the FIFO upon receipt of the time code data. U.S. Patent 5,155,510 discusses conditioning the output of the digital sound source in a dual digital/analog motion picture theatre sound system so that the digitally derived audio source emulates the analog signal. Finally, U.S. Patent No. 5,751,398 discusses how digital time code corresponding to locations of the filmstrip is applied and used to read out digitally stored audio data in a manner that can accommodate breaks in the film, projector changeover, various time code validation schemes and allow the use of a relatively slow, but highly reliable data store device such as a digital audio tape (DAT) player. [0010] U.S. Patent 5,450,146 also assigned to Digital Theatre Systems discusses a method of encoding a synchronizing signal within a traditional analog sound-on-film track. The additional encoding does not replace the normal sound track but exists within it, so that both a separate digital or the analog on film sound track can be employed in the motion picture theatre. [0011] U.S. Patent 4,839,733 by Karamon et al. makes use of the analog soundtrack on the edge of the filmstrip to provide synchronization information without the need to add any additional information. The high quality digital soundtrack is made from the same master recording as the analog track so that there is a precise correlation in the information content of the two sound tracks. Correlation between the two is achieved by re-iterative subtractions between the absolute value envelopes of the two soundtracks. Like the DTS system this method allows the use of a fall back analog track in case of a failure within the digital sound track system, and is advantageous in that no extra processing step is required in production of the filmstrip. [0012] U.S. Patent No. 5,877,842 assigned to Daily Disc Licensing describes a system for synchronizing and viewing the daily filming of a plurality of diverse film segments with their matching audio files by using manufacturer supplied barcode on the edge of film as an indexing means to log the location of audio-visual synchronization points (i.e. typically when a sound clapper is filmed at the start of a filming sequence). A bar code reader measures the progress of film through the projector and transmits barcode information to a computer where digital audio files corresponding to the film segments are retrieved and played in synchronism with the projected image segments. [0013] The use of a soundtrack, whether analog or digital that is separate from the motion picture film is advantageous in that it allows the use of a higher quality audio than is possible to place on the limited area on the edge of a moving strip of film. Attempts to increase the amount of audio data present on the edge of the film such as the recent digital audio on film systems such as CDS and SDSS have not been successful in the motion picture industry. Another advantage of having the sound track separate from the motion picture film is that in the event of damage to the filmstrip in which film frames are lost, repairs can be made by splicing a so-called black slug into the filmstrip and only the visual appearance of the film is compromised; the audio data, because it is stored separately is unaffected by the lost of film frames. Seeing a few moments of blackness, while noticeable, is much less disturbing to motion picture audiences than having a discontinuity in the sound track. [0014] A disadvantage of having separate sound tracks is that a more complicated system of synchronizing the visual and audio is required. The method used by DTS, writing a digital time code onto the edge of the film is an effective method for the standard 35mm motion picture industry. It is relatively robust; allows the retention of a back up analog sound track on the edge of the film; and it can be written on the edge of the film during the processing stage when the traditional analog sound track is added so the method is not prohibitively expensive. There are however significant differences between the equipment and requirements of the large format motion picture industry that limit the effectiveness of a synchronizing system like DTS's. [0015] One of the greatest differences between the traditional 35mm based motion picture industry and the large format motion picture industry is the cost of the film prints that producers and exhibitors must pay. In the case of Imax, which uses 70mm print film and a 15 perforation image, the amount of image area per frame is roughly ten times that of 35mm. Film stock and processing are therefore correspondingly greater than that of 35mm film. Placing a digital time code on a large format print will further increase print cost. Print costs are already a large cost to exhibitors. It is partly for this reason that Imax decided early to have the soundtrack separate from the film print. In addition, there are far fewer exhibitors in the large format industry so the setup (non-recurring) costs for additional processing are not amortized over large numbers of theatres as they are for the 35mm film industry. [0016] Another difference between the conventional 35mm film industry and the large format industry is that the working life of large format film prints is significantly longer than 35mm film prints. Many large format films tend to have destination or educational themes that have a timeless appeal unlike the hit driven dynamics of conventional Hollywood motion pictures. As a result, large format films tend to be used for 3,000 passes or more compared with several hundred for 35mm prints. Because of this extended print use, there is some risk that an optical digital time code placed on a high wear area at the edge of the film may become prematurely deteriorated to the point of failure. [0017] Yet another difference between the conventional and large format industry is that the latter occasionally has the possibility of exhibiting 3D motion pictures in projectors that have two separate film strips, one for each eye, running simultaneously. These filmstrips must be kept synchronized to each other as well as to the external sound track. This film-to- film synchronization could be achieved by encoding each filmstrip with digital time code, but the cost would be exorbitant. [0018] The standard method of synchronizing visual images with separate sound tracks in Imax or other large format equipment has been reliable and effective, but recent changes in the industry have created the need to improve upon an electromagnetic link between the projector and the sound playback equipment. There is growing demand to exhibit Hollywood style motion pictures in large format theatres located in conventional cinema multiplexes, and the level of training and skill of the projectionists in these venues is somewhat below that of the highly trained Imax projectionists found in museums, educational centres and destination attraction institutions. With inexperienced projectionists there is a greater probability that sound synchronization could be lost because of: incorrectly assembled film sequences; incorrect film trailer combinations; damaged or incorrectly repaired films; and matching the wrong soundtrack with the film. A further problem that is more probable with inexperienced staff is an incorrect film splice that leads to an image being one or more perforations out of frame. Summary of the Invention [0019] Embodiments of the present invention comprise synchronization check systems and methods that may be added to and integrated with an existing primary method of synchronization. In one embodiment, the synchronization check system does not provide a continuous stream of synchronization information, but does systematically provide periodic data identifying specific perforations on the edge of the film print. The source of the identifying data on the edge of the film is film manufacturer's periodic edge code and is read by a suitable edge code reader. Data provided by the synchronization check system is compared with an existing look-up table that lists the film's edge code values that correspond with the projector generated frame count values. If there is a mismatch or error between the frame count value in the look up table with the actual frame count being generated by the projector at the actual edge code then there is a synchronization error between the film and the sound track or between the left and right eye film strips. At this point a decision is made, dependant on the nature of the error, and corrective action can be taken to synchronize the projected images and the sound track or the left and right images. In addition to acting as a monitor for synchronization, the film position data gathered by the system can also be used to assist in monitoring and adjusting the film frame position in the projection gate for film start frame setup and during the presentation.

Brief Description of the Drawings [0020] These and other features, aspects, and advantages of the present invention are better understood when the following Detailed Description is read with reference to the accompanying drawings. [0021] Figure 1 is a general block diagram of one embodiment of a synchronization check system. [0022] Figure 2 illustrates prior art sound-on-film schemes as well as a prior art time code (DTS) system. [0023] Figure 3 illustrates a film manufacture's edge code that may be used in the inventive synchronization check system. [0024] Figure 4 is an overview of a motion picture film projector, such as a traditional rolling loop projector, illustrating an illustrative location of an edge code reader in relation to the main projector components. [0025] Figure 5 is an illustrative embodiment of a data structure of an edge code look up table (LUT) that may be used by the synchronization check system to monitor film position in the projection gate as well as monitor and maintain synchronization between the film and the external audio source and/or between left and right eye film strips. [0026] Figure 6 illustrates a typical frame of film showing a position of a Keykode perforation identifier below a perforation according to one embodiment of the invention. [0027] Figure 7 is an overview of an illustrative motion picture film projector that features a novel film advance mechanism which when combined with the synchronization check system allows the projector to perform enhanced film positioning capabilities.

Detailed Description [0028] Embodiments of the present invention comprise robust synchronization check systems and methods that can be used to check image and soundtrack synchronization that are reliable even in situations where the skill and experience level of a projectionist is not high. Embodiments of the synchronization check systems and methods may be used to provide enhanced projector operating features that include: using of the standard SMPTE leader with Keykode to facilitate automatic loading of the film in the projector so that the start frame is automatically positioned in the film gate; the ability to incrementally adjust the position of the film in the projection gate in real time to automatically correct for a misalignment between a film frame and the aperture; automatic identification of key locations on a film for show automation; validation of the sound track with the film print; the ability to easily make changes in the composition of the film strip without undue risk of losing audio visual synchronization; and the ability to synchronize two separate stereoscopic filmstrips during real time to correct any temporal misalignments between left and right eye images. [0029] The synchronization check system may be used as a back up method of visual audio synchronization in case the primary method of synchronization malfunctions during a presentation. Embodiments of the synchronization check systems and methods do not require any additional information to be written onto the edge of film prints and thus, may provide these features at a low cost. [0030] Referring now to Figure 1, an illustrative control system 1 for a theatre presentation system to ensure synchronization between film data and audio data is shown as a block diagram. The theatre presentation systems can comprise a projection system, a sound system, and a screen system. The audio playback system is a portion of the sound system and the projector control system is a portion of the projection system. The primary synchronization scheme comprises elements 2 through 5 and involves a shaft encoder 2 located on the projection system that during operation sends bi-phase pulses to a count accumulator 3. Based on the pulses, the count accumulator 3 determines an accumulative frame count, and sends the frame count to a time code generator 4 that generates an SMPTE time code to drive the audio playback system 5. [0031] The synchronization check system that augments the primary system is indicated by elements 10 through 12. An edge code reader 10 located on the motion picture projector upstream of the projection gate reads the film manufacturer's edge code in real time as film is fed into the projector from a supply reel. In one embodiment, the system uses print film from Eastman Kodak whose edge code is known by the brand name of Keykode. It should be noted that other film manufacturers also include edge code on their cinematic film stocks that can also be used by the synchronization system in other embodiments. [0032] Keykode edge code is in barcode form. Edge code reader 10 must be able to read barcodes accurately at high speeds, i Jn one embodiment, nine times per second as there are three barcodes for every 8 film frames (and the projector frame rate is 24 frames per second). A suitable edge code reader 10 is laser based barcode reader model MS-3 as supplied by Microscan Systems Inc. [0033] Edge code data from edge code reader 10 is supplied to a comparator and match engine 11. The edge code data can provide the absolute position of the film. The comparator and match engine 11 also receives a corresponding frame count (accumulated amount of film) from a count accumulator 3. The comparator and match engine 11 compares the received edge code data and the corresponding frame count with values in an existing look up table (LUT) 12. The values in the LUT 12 are generated automatically when the film is run through the projector for the first time. The LUT 12 provides a correspondence between edge code data and frame count. The comparator and match engine 11 can compare the real-time edge code and the real-time frame count to the LUT 12 to determine if there is a mismatch or error. " For example, the comparator and match engine 11 can match up the real-time edge code to the same edge code in the LUT 12 and then determine if the real-time frame count is the same as the frame count corresponding to the edge code in the LUT 12. If the real-time frame count differs from the frame count in the LUT 12, then the comparator and match engine 11 determines that an error has occurred and the projection system needs to be re- synchronized. [0034] If the comparator and match engine 11 determines an error, then corrective action can be initiated for the theatre presentation system by the comparator and match engine 11. The comparator and match engine 11 may cause adjustments to be made in the projector or the audio playback system of the theatre presentation system so that the projected images are resynchronized with the soundtrack. For example, the comparator and match engine 11 may cause the projector to slow down or speed up by sending the appropriate control signals to the projector control system 13. If the adjustment is made by changing the projector speed, the comparator and match engine 11 sends a correction signal to time code generator 4, which overrides the projector-generated time code thereby allowing audio playback system 5 to continue playing the soundtrack without being affected by the corrective speed changes of the projector. Once the projector is back in synchronism as determined by an edge code match using the LUT 12 as described above, the audio playback system synchronization reference reverts back to the frame counts generated by the projector. [0035] Referring now to Figure 3, the edge code 31, or Keykode (in barcode form) as used by Eastman Kodak is illustrated on a segment of 65mm negative motion picture film 30. Large format motion picture cameras and recording devices generally use 65mm film. The images of the 65mm negative film eventually become transferred onto 70mm film prints for use in large format film projectors. Keykode is a latent image placed onto the edge of filmstrips as they are manufactured by Kodak in a non-repeating manner. The Keykode images become visible after developing film negatives and because they are non-repeating they uniquely identify each segment of film. On 65mm negative film, there is a unique, cumulative 4 digit number every 120 perforations, or 8 Imax (15 perforation) film frames. The zero reference mark 32 denotes the first perforation in each unique set of 120. The Keykode barcode occurs every 40 perforations, its count is comprised of four digits that increment every 120 perforations. The offset of the film frame line 33 with respect to the Keykode barcode 31 is initially established in the first run of the film in which the system records the offset between the known start film frame line and the position of the last few Keykode number reads leading up to the start frame. Once the start frame offset with respect to the barcode is known, the subsequent offsets can be determined within the first run for the Keykode sequences associated with the all scenes in the film. This data is stored in the LUT 12 (in figure 1). [0036] Given that the Keykode count sequence increments every 120 perforations and the encoder 2 (in figure 1) can resolve film position to within a film perforation it becomes possible to do a number of synchronization checks with the system within the accuracy of a film perforation. One check involves the audio playback system following the counts from encoder 2 (in figure 1) whereby it becomes possible to check that the sound matches up with the specific image frame marked by the Keykode number being read. Another check that becomes possible is to confirm the timing between the amount of film that has passed by as sensed by encoder 2 (in figure 1) matches the absolute film position marked by the Keykode number being read. Should an error occur in these situations, for example due to improper film splicing repair that results in missing or additional frames, the system can detect such errors and take appropriate action. [0037] Referring now to Figure 4, an illustrative rolling loop motion picture projector of the kind commonly found in large format motion picture theatres is schematically depicted at 40. The filmstrip 41 from a film supply unit is driven by an input sprocket 43 into the gap between rotor 46 and the stator segments 48. Film loops are intermittently created and fed into rotor gaps 50 at the projection rate of 24 frames per second and transported by the rotor towards a projection gate 47. A cam driven deceleration mechanism 44 is located near projection gate 47 to slow down the film before it is registered on fixed registration pins (not shown) at the aperture 49. After a new film frame is registered at the aperture the film loop that carried it is transported away by the rotor gap until it decays before an output sprocket 45. Edge code reader 42 is located before input sprocket 43 and sends data to the comparator and match engine 11 (shown in block diagram in Figure 1) which upon detection of a misalignment between the filmstrip and the corresponding frame position in the LUT 12 sends a corrective drive signal to the projector control system 13 or the time code generator 4 (in figure 1) to either speed up or slow down the projector or audio playback respectively until the images and soundtrack become synchronized within a fraction of a frame again. It should be noted that when the system 1 is used with this type of projector featuring a mechanically timed deceleration cam, the response of the system to an indication of misalignment may be inhibited by the inertia of the rotating mechanisms. The inertia of the mechanism includes the inertia of the rotor, the deceleration cam, the input, and the output sprocket, which may be all mechanically driven by one common motor. [0038] Referring now to Figure 5, a simplified illustration of the contents of a typical look up table (LUT) used by the inventive system is indicated generally by 100. A unique filmstrip identifier is stored in header 101, and unique edge code (such as Keykode) values 102 are stored in an array and are linked logically with a matching column of frame count numbers 103. Frame count 103 may also be a perforation count. The frame count numbers are generated by the bi-phase pulses from encoder 2 (shown in Figure 1) while the edge code (Keykode) values are generated from edge code reader 10. The edge code values shown in Figure 5, kθ, k40 etc., are not the form of the values that would actually be stored in the LUT; instead they would be the unique alphanumeric codes written on the edge of the fϊlmstrip at the time of manufacture. The frame count numbers 103 can be translated into perforation counts since each image frame starts 15 perforations from the previous frame. For example, the frame counts 103 could be written as perforation counts 1, 16, 31, 46, etc. [0039] The data stored in LUT 100 can be generated the first time the filmstrip is run through the projector. Figure 1 does not specifically show this configuration but there are a number of ways that the accumulated count from the encoder 2 and the edge code reader 10 data for the LUT may be retrieved and stored in the show controller 14. In one embodiment, the LUT data is generated and verified at a show print source location and the information distributed via a storage medium such as a disk with each film print sent to each theatre. This can save theatre operators from having to carry out the first time pass to generate the LUT data. It is also possible to generate and verify the LUT data at the theatre by simply putting the synchronization check system in a mode that records all the accumulated frame count information that corresponds with the recorded edge code count information in the show control. Each time a particular show of interest is being presented the show control 14 can load the corresponding first pass LUT data into the edge code LUT 12. [0040] Figure 6 shows a section of a filmstrip 60 and an edge code perforation marker 64 at a position five perforations from the edge of frame 61. A frame line 63 marks the edge between frame 61 and the adjacent frame 62 that represents frame N+l. Since both the edge code values and the bi-phase pulses generated by encoder 2 refer to specific perforations from the start of a motion picture (every 40th perforation is marked by an edge code (Keykode) identifier), an exact correspondence between the edge code values and the bi-phase pulses stored in LUT 100 can be generated and maintained. For example, each of the first five perforations in frame N can be given unique positional addresses based on the value of the fifth perforation that corresponds to the edge code value of perforation marker 64. The first perforation of frame N would be the value of marker 64 minus 4, the second perforation the value of 64 minus 3, etc. Similarly the address of the sixth perforation in frame N would be the value of marker 64 + 1 and so on. [0041] Figure 7 depicts schematically a novel rolling loop projector that is the subject of applicant's co-pending PCT patent application PCT/IB2005/001049 entitled "Electronically Controlled Film Transport Methods and Systems," filed April 20, 2005, which is hereby incorporated by this reference. It features a novel deceleration mechanism that works synergistically with the novel synchronization check system to provide the capability of fractionally repositioning a film frame in the projector film gate 75 automatically during a presentation. Film 41 is fed into the gap between the rotor 78 and stator segment 73 by the combined action of an electronically controlled constant speed input sprocket 71 and a variable speed feed sprocket 72. The use of electronically controlled sprocket 72 eliminates the need for the standard cam driven mechanical film deceleration mechanism 44 of figure 4, and allows the real time adjustment of relative frame position one perforation at a time by feeding undersized (e.g. 14 perforation) or oversized (e.g. 16 perforation) film loops into the passing rotor gaps. Edge code reader 42 can provide the initial control information to the synchronization check system that in turn provides the signal to the projection control system to initiate the corrective action to be done by the electronically controlled sprockets 71, 72, and 76. For example, if edge code reader 42 read an edge code value that was 10 perforations out of synchronization with the frame perforation count number provided by the shaft encoder, a control signal is sent to the projector control system. The projector control system can provide the corrective control signal to the electronic servo motor driving sprocket 71, 72, and 76 to feed 16 perforations of film into 10 consecutive rotor gaps until the film images were properly positioned in the projector film gate 75. In this example, the film frame repositioning in the film gate takes place during the presentation and this correction may be achieved in slightly less than 0.5 seconds. [0042] Another example is if the edge code reader 42 reads an edge code value that is 10 frames out of synchronization with the frame count number provided by the shaft encoder. In this situation, a control signal may be provided to speed up or slow down the projector via the projector control system (block 13 in figure 1) or the audio playback system (via the Time Code Generator 4 in figure 1) to re-establish synchronization between images and soundtrack. [0043] In another embodiment, the synchronization control system may be used to automatically synchronize separate left and right eye filmstrips in a two-filmstrip stereoscopic motion picture projection system. In such a system, each filmstrip may have it's own edge code reader and sends edge code data to a system comparator and match engine. The comparator and match engine can compare the current edge code data and frame count data to a previously generated Stereoscopic Match Look Up Table (SMLUT). If either of the current edge code values differed from what was expected, control signals would be sent to one or both of the projector control systems to re-establish temporal synchronization between the left and right eye film strips. [0044] Other novel and advantageous benefits are possible with the combination of having electronically controlled sprockets and edge code based synchronization check system. One such benefit is having the ability for the projector to automatically position the motion picture start frame (the designated number one frame from which the count accumulator 3 in figure 1 starts accumulating frame counts) in the projector film gate. To do this, a pre-designated edge code value that occurs before the start frame is stored in memory. When film is loaded into the projector and the pre-designated edge code number is read by the edge code reader the projector controls the film advance an exact number of perforations until the start film frame is positioned precisely in the aperture of the projector film gate. [0045] Another possible advantageous benefit is the ability to automatically re-frame the film with respect to the aperture in the projector film gate if it ever becomes misaligned with respect to the aperture by one or more perforations. [0046] In another embodiment, the synchronization control system and method may allow for the automatic generation of show control signals. For example, at a pre-specified edge code value, a control signal can be generated and sent to dim the house lights in the theatre. [0047] The system may also provide an insurance function by being able to provide backup such as with picture and sound synchronization control in case the primary system (the shaft encoder) should fail during the presentation. Another valuable benefit of the inventive system is that it allows a projector operator to easily make changes in the composition of the filmstrip without undue risk of losing the picture and sound synchronization. [0048] The inventive system and method may provide some or all of the above features and benefits at a low cost and without the need for any additional information to be written onto the edge of film prints. This is different than other systems that rely on a code being added to the film at some stage after the film has been purchased from the film manufacturer. [0049] In one embodiment, a synchronization check method is capable of using film that has the film manufacturer's film edge code to synchronize a theatre presentations system comprising a film projector and an audio playback system. An absolute film position can be determined by reading the film manufacturer's code on a film edge. An accumulative amount of film can be determined from a film position sensor. An error can be determined between the accumulative amount of film that passes the film position sensor and the absolute position of the film determined by reading the code on the film. If an error is determined, the resulting error can be used to initiate corrective action in the projection system. The corrective action can be performed during the film presentation. The method can be used to check synchronization between picture and sound and initiate corrective action to re-establish synchronization in the event an error should occur in the picture and sound synchronization. [0050] The foregoing description of embodiments of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated.