EP0051584A1

EP0051584A1 - Process of mastering audio and video using motion picture techniques

Info

Publication number: EP0051584A1
Application number: EP19800901435
Authority: EP
Inventors: Robert C. Fine
Original assignee: MAGNA-TECH ELECTRONIC Co
Current assignee: MAGNA-TECH ELECTRONIC Co
Priority date: 1980-05-12
Filing date: 1980-05-12
Publication date: 1982-05-19
Also published as: AU6128380A; WO1981003406A1

Abstract

Procede de synchronisation d'informations audio et video ou des techniques d'images en mouvement standard peuvent etre utilisees pour former une piste audio maitresse finie synchronisee avec un signal video enregistre Une bande video standard maitresse est enregistree (12) avec un code de temps conventionnel SMPTE ou autre code identifiant chacune des images enregistrees. Le signal video et le code de temps sont transferes sur un premier film magnetique a perforation (29) qui fonctionne a des vitesses d'images en mouvement standard. Ce film sert d'impression "de travail" qui est ensuite utilisee pour produire une pluralite de pistes audio qui sont synchronisees avec les informations video apparaissant sur l'impression de travail. Ensuite, les pistes audio sont melangees pour former une piste audio maitresse finie sur un second film magnetique a perforations. Le code de temps SMPTE est transfere de l'epreuve de travail sur le second film magnetique a perforation en synchronisme avec la piste audio maitresse finie. La piste audio maitresse finie est ensuite transferee en synchronisme sur la bande video maitresse, les codes de temps stockes SMPTE etant utilises (14) pour entrainer le film audio et la bande video en synchronisme.Method for synchronizing audio and video information or standard moving image techniques can be used to form a finished master audio track synchronized with a recorded video signal A standard master video tape is recorded (12) with a conventional time code SMPTE or other code identifying each of the recorded images. The video signal and the time code are transferred to a first magnetic perforation film (29) which operates at standard moving image speeds. This film serves as a "working" impression which is then used to produce a plurality of audio tracks which are synchronized with the video information appearing on the working impression. Then, the audio tracks are mixed to form a finished master audio track on a second magnetic film with perforations. The SMPTE time code is transferred from the working test to the second magnetic perforated film in synchronism with the finished master audio track. The finished master audio track is then transferred in synchronism to the master video tape, the stored time codes SMPTE being used (14) to train the audio film and the video tape in synchronism.

Description

PROCESS OF MASTERING AUDIO AND VIDEO USING MOTION PICTURE TECHNIQUES _

This invention relates to a method of synchro¬ nizing audio and video information. More specifically, the present invention relates to a process for producing a video tape of the type used in television broadcasting wherein motion picture techniques for synchronizing sound and video may be employed without sacrificing the advan¬ tages of modern video editing procedures. Background of the Invention In the early days of television, most programs were live or optically recorded (kinescoped) on conven¬ tional motion picture film. When a program was first recorded on motion picture film, conventional motion picture techniques for editing and synchronizing the sound and visual tracks could be used.

Technological advances in the art of recording video information have increased the desirability of recording television programs on video tape directly. This requires that the video be edited to provide the desired visual effect and also that a sound track be prepared in which the sound effects and dialogue are exactly synchronized with the recorded video.

In recording on video tape, it is common prac¬ tice to record a time code identifying each recorded frame on the tape medium. The standard time code used worldwide is referred to as the SMPTE time code which comprises an 80-bit code of which 40 bits are used to identify the recording time (in hours, minutes and seconds) for each frame and the number of the frame on the tape. The use of this SMPTE time code has enabled sophisticated computer controlled techniques for editing video signals and, currently, the editing of video tape is more efficient than the editing of motion picture film wherein various film effects must be spliced together to provide a finished product. Despite the sophistication of currently avail¬ able video editing techniques, there is a problem in synchronizing an audio track with the recorded video. Principally, this is because the engineer responsible fo mixing the audio is unable to rely on the visual appear¬ ance of the recorded video ape. As an example, in producing a video tape, it may be necessary to synchroniz music tracks, dialogue tracks and tracks containing various types of sound effects. Each one of these track (sometimes referred to as a sound mixing element) must b prepared using a time lock system dependent on the recor ded SMPTE time code so that the audio and video signals are synchronized exactly. In practice, this is a very expensive undertaking since costly mixing equipment must be used to synchronize and prepare the mixing elements o a multi-track tape. Because of the expense involved in revising a recorded element or track, as a practical matter, artistic compromises frequently arise in cases where a director is partially dissatisfied with one or more of the mixing elements. Moreover, the inability of the director or editor to "feel" the visual medium with which he is working as the sound track is created dim¬ inishes the feeling of an artistic or creative contribu¬ tion. All of these factors have limited the acceptance industry of direct video recording of television programs Objects of the Invention

The principal object of the invention is to provide a simplified and inexpensive method of synchro¬ nizing audio and recorded video signals. A more specific object of the invention is to enable the use of conventional film synchronizing tech¬ niques for post production sound mixing of video tapes. Brief Summary of the Invention

Briefly, in accordance with the invention, a master edited video tape is prepared containing a video signal and a recorded time code identifying each frame. The video signal is then transferred to a first sprocketed magnetic film which may operate at a standard motion picture speed. Using this film as a work print, a plur¬ ality of audio tracks are produced in synchronism with the video information recorded on the work print. Thereafter, the recorded audio tracks are mixed to form a master finished audio track which is recorded on a second sprocketed magnetic film together with the time code of the original master edited video tape. The audio and video signals may then be combined by using the recorded time codes on the finished audio film and the master edited video tape to drive them in synchronism as the audio is transferred to the video tape. The Drawings Figure 1 is a flow chart showing the steps involved in practicing the invention;

Figure 2 is a block diagram showing the means for synchronizing the master edited video tape and the master finished audio film; and Figure 3 is a diagrammatic illustration showing the layout of a video tape machine modified to record on and reproduce from a sprocketed magnetic film. Detailed Description

The process according to the invention contem- plates the use of conventional video editing techniques in conjunction with motion picture sound synchronizing techniques. Although there is no known commercially available apparatus for performing the process of the invention, the modifications of existing devices required to practice the invention will be apparent to those of ordinary skill in the art in the light of the following description. Accordingly, this specification does not include a detailed description of the physical construc¬ tion of the various devices and machines used to practice the invention.

The following description may be read in con¬ junction with the flow diagram of Fig. 1 in which the

OMPI /λ_f. WIPO ^" various steps of the invention are recounted sequentially from top to bottom.

In "practicing the invention, it is necessary to first produce (or have produced) a master edited video tape. Conventionally, this may be accomplished by the us of a number of cameras recording a given scene from different angles. At the same time, an audio track containing the dialogue of the scene involved is recorded in conventional fashion on the tape. The director then edits the recorded video, most advantageously by computer ized editing equipment, to produce a master edited video tape. Typically, the video is recorded by quadraplex scanning techniques on two-inch magnetic tape or by helical scanning techniques on one inch magnetic tape about .5 mils thick.

It is frequently the case that the audio as recorded is unacceptable because of background noise or improper microphone placement. Similarly,, in many cases the audio track is incomplete because it contains no musi or special sound effects. Accordingly, as a part .of the editing process, it is necessary to build a finished audi track which contains the necessary dialogue, music and sound effects. Obviously, the audio track, including all of the separate parts which make up that track, must be accurately synchronized with the video.

In accordance with the invention, the contents of the master edited video tape (video, SMPTE time code, and audio) are transferred to and recorded on a sprocket driven magnetic film which thereafter serves as a work print. The magnetic film has the width of conventional movie film and is driven at the corresponding conventiona speed. For example, in the case of 16 mm film, the film will be driven at a speed of 36 feet per minute (24 frame per second). In the case of 35 mm film, the film moves a 90 feet per minute. Obviously, the selection of film speed does not constitute a feature of the invention but

OMPI _/fr_ WIPO the foregoing are preferred for purposes of convenience. In the case of a 16 mm film, the video signals are re¬ corded on a portion of the film which is one-half inch wide. The audio track will be recorded just inside the sprocket holes and the conventional SMPTE time code will be recorded outside of the sprocket holes. The control track containing the vertical sync pulses which synchro¬ nizes the speed of the scanning mechanism will be recorded on the edge of the film opposite the sprocket holes. Conventionally, a separate tape or film of the audio is made at the same time so that a high quality dialogue track will be available for subsequent mixing and/or synchronizing.

Standard magnetic tape for video recording purposes is about .5 mils thick. This tape cannot con¬ veniently be handled manually because it is so thin. Accordingly, in the preferred embodiment of the invention, the thickness of the magnetic films is in the order of 3 mils which enables the film to be conveniently handled. In one embodiment of the invention, the 3 mil .sprocketed magnetic film was a 16 mm film, driven at a speed of 36 feet per minute. The video recorder/reproducer was a Panasonic helical scan device modified by replacement of the drive mechanism with a standard sprocket wheel move- ment. Because of the variation in speed, it was necessary also to vary the speed of rotation of the scanning unit so that the scanning unit would lay down successive fields as the tape was moved by the sprocket drive mechanism.

The work print created as described above is next used to "build" the audio tracks containing the dialogue, sound effects, and music. Typically, there may ^'be from one to four dialogue tracks, one to four music tracks and from one to ten sound effect tracks. Each track is recorded on a separate film and, ideally, the tracks are maintained separate until the final mixing since this, as is well-known, increases the flexibility of the overall system.

The same apparatus used to record the work print can be used to play back the work print to build the audi tracks although it is anticipated that in practice a second recorder/ reproducer will be used for this purpose since the audio tracks will usually be formed in a separ¬ ate editing area. In any event, a video screen will be provided so that any selected portion of the work print can be replayed enabling reproduction of moving or still images. The ability to replay any selected video frame is a common feature on many commercially available video tape reproducers.

The sprocketed video film will include the SMPT time code indicating the first frame of the program material. In use, the editor will mark this first frame on the work print so that he has a visibly recognizable starting point on the magnetic film. The audio tracks will then be built in the same fashion as such tracks are built in the production of a motion picture film.

This is done by maintaining a fixed physical relationship between each of the audio tracks (films) containing the diverse audio effects. There are various available editing machines for this purpose. For example, pulse controlled motors may drive sprocket wheels which engage the sprockets of the individual tracks, with optical encoding disks fixed to the output shafts of the motors generate the pulses used to maintain fixed relationships between each of the tracks and, of course, the video track. In accordance with the invention, this fixed relationship to the video information can be maintained even though it is in the form of a magnetically recorded signal because the signal is recorded on a sprocketed magnetic film at the same speed at which sound editing takes place (e.g. conventional motion picture film speed) . The sound editor runs the film and splices any desired sound effect, dialogue or musical effect onto any one or more of the sprocketed tracks which have been running in synchronism with the video film from the starting point. During sound editing, the editor need not consider television frame measurement and need only concern himself with film footage as is conventionally done in editing motion picture films. This is highly advantageous because of the editor's familiarity with the practice, its relative simplicity, and also because of the direct "hands on" control which is generally preferred, from a creative point of view.

A full description of the sound editor's func¬ tion in building the separate audio tracks is not con- tained herein since, in accordance with the preferred embodiment, the operation is essentially the same as that which takes place during motion picture film sound editing.

The mixing or final combining of the audio tracks takes place in a mixing room. In this operation, each of a plurality of sprocket-driven audio playback machines (each containing one or more audio tracks) is locked to the others by an optical encoder or any other suitable synchronizing means (e.g. selsyn controlled motor or crystal controlled interlock). The sprocketed video recorder is likewise locked to the audio playback machines, as is a sprocketed audio film recorder on which the mixed sound track is to be recorded. The recorded video from the work print^* is displayed on a monitor screen during mixing. In conventional fashion, the mixing engineer combines all of the individual audio tracks (with approp¬ riate volume control, fades, etc.) into a master finished audio track on the audio film recorder. Since all of these tracks are driven in synchronism from the same starting point, the master finished audio track will have the desired relatioip to the video with appropriate sound effects as selected by the mixing engineer. During the mixing operation, the SMPTE time code is transferred from the work print to a separate track on the sprocketed film which contains the master finished audio track.

Thus, the sprocketed film contains both the master fin¬ ished audio track and a SMPTE time code which represents the video frames corresponding to the audio track.

The final step is to "lay back" the master finished audio track to the master edited video tape. Fo this purpose, the master audio finished film is threaded onto a sprocketed reproducer having outputs which generat an audio output signal together with a regenerated SMPTE time code. The audio film is then brought to the startin point on the film (which has been visibly marked on the film) . It is now possible to transfer the master finishe audio track to the non-sprocketed video tape if the tape and film are locked together so that the audio track remains in exact synchronism with the video. In accor- dance with the invention, such synchronism is maintained by a comparison of the SMPTE time codes appearing on both the tape and film.

Figure 2 shows diagrammatically how the master finished audio track is synchronized with the master edited video tape. The master finished audio, recorded o sprocketed film, is placed on a conventional audio repro¬ ducer 10 and the master edited video tape is placed on a video tape machine 12. The SMPTE time codes from both th master finished audio track and the master edited video tape are regenerated and fed to a comparator 14, which generates a servo control error signal when the SMPTE tim codes are not the same. This error signal is then used t control the speed of the video tape so that the film and tape are driven in exact synchronism. The master finishe audio track may then be recorded on the master edited video tape in place of the existing audio track. Since

O the audio has been synchronized with the SMPTE time code, it will then be exactly synchronized with the recorded video. There is no need to compensate for differences in speed between the audio film and the video tape becuse the SMPTE time code is employed as the synchronizing means.

A video screen 16 and a loud speaker 18 may be used to monitor the video and audio tracks, respectively, during the final combining step.

Although the use of the sprocketed work print is a principal feature of the invention, the invention is not limited to standard motion picture size film or even to standard motion picture speeds although these, of course, are highly preferred because of the adaptability to current machines. Figure 3 shows in partially schematic form, the physical layout of the various parts of a video film recorder which was used to record a video work print on sprocketed magnetic film.

A helical video scanning head 20 is mounted conventionally with its axis at an angle so that the tape (or film) is scanned helically. The machine includes a video erase head 22, an audio erase head 23, and an audio record/piayback head 24. In the modification of the apparatus used in practicing the invention, a SMPTE code read/write head 25 is provided to read or write the

SMPTE time code between the sprocket holes and the edge of the film.

The driving mechanism comprises a standard film drive sprocket 27 cooperating with a sprocket shoe 28. The sprocket drive mechanism is shown diagrammatically since it may be (and preferably is) a standard mechanism of the type used to drive movie film.

The magnetic film is shown at 29 with arrows indicating the direction of movement. Thus, the film is wrapped around the top of sprocket 27 passing the video erase head 22 and around the helical scanning head 20

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:_\ ~ ΪFδ^~~ (from top to bottom) where it passes the heads 23, 24 and 25, then over a pressure idler 26 and back around the sprocket 27 to a take-up spool. The idler 26 is moved by a rotary solenoid (not shown) to exert pressure against film 29 in the PLAY mode, whether in forward or reverse directions. This controls the tension applied by the fil to the scanning drum. For high speed operation, the idle is moved to release the tension.

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Claims

WHAT IS CLAIMED IS:

1. A method of synchronizing audio and video tracks, comprising preparing a master edited video tape including a recorded time code identifying each recorded frame, transferring at least the video data and the time code from the master edited video tape to a first sprocketed magnetic film operating at a predetermined speed, building a plurality of audio tracks synchronized with the video information appearing on said first sprocketed magnetic film, and mixing said audio tracks to form a master fin¬ ished audio track on a second sprocketed magnetic film and transferring said time code from said first to said second sprocketed magnetic film in a predetermined relationship to said master finished audio track.

2. A method of synchronizing audio and video tracks according to claim 1 , including the step of laying back the master finished audio track onto the master edited video tape by comparing the recorded time codes and synchronizing the movement of said master finished audio track and said master edited video tape as a function of the comparison.

3. A method of synchronizing audio and video tracks according to claim 1 or 2, wherein said predetermined speed is a standard motion picture speed.

4. A method of synchronizing audio and video tracks according to claim 1 wherein said plurality of audio tracks are built on sprocketed magnetic film while displaying the video information recorded on said first sprocketed magnetic film.

5. A method of synchronizing audio and video tracks comprising transferring at least the video signal from a video tape to a first sprocketed magnetic film operating at a pre¬ determined speed, using said sprocketed magnetic film to build audio tracks synchronized with the video information appearing on said sprocketed magnetic film, and thereafter combining at least the video from said video tape and the synchronized audio tracks in synchronism.

6. A method of synchronizing audio and video track according to claim 5, wherein a time code is transferred from the video tape to said sprocketed magnetic film, and further including the step of mixing the synchronized audio tracks and adding thereto the time code appearing on said sprocketed magnetic film for use in synchronizing said video tape and aud tracks during said combining step.

7. A method of synchronizing audio and video track according to claim 5 or 6, including the step of monitoring the video information appearing on said sprocketed magnetic film while said audio tracks are being synchronized and during said combining step.

8. A method of synchronizing audio and video track according to claim 5 or 6, wherein said sprocketed magnetic film is operated at a standard motion picture film speed.

9. A method of synchronizing audio and video track according to claim 5, wherein said sprocketed magnetic, film is approximately three mils thick.

10. A video recording/reproducing machine for use in editing video tapes, comprising: a scanning drum including video recording/ reproducing heads for recording or reproducing video signals on a magnetic film have sprocket holes on at least one side, an audio record/reproduce head for recording or reproducing audio signals on a track between the video signals and said sprocket holes, a SMPTE time code head for recording or repro¬ ducing time code signals on a track between said sprocket holes and the adjacent edge of the film, and a sprocket drive mechanism for moving said sprocketed film past said scanning drum and heads.

11. A video recording/reproducing machine accordin to claim 10, wherein said sprocket drive mechanism moves said sprocketed film at a standard motion picture film rate.