Film and Video Speed – what?

Film and Video Speed

Film / Video post speed/frame rate issues…

Before you start a sound project find out the:
1. frame rate
2. project speed
3. post production life cycle
A. how the project was shot
B. how the project was captured
C. how the project was edited
D. how the project was exported for audio edit
E. format the client wants you to work

The first question to ask when dealing which projects: is the picture frame rate in sync with 48kHz. If so there will be no need to do a sample rate conversion or digitize via analog sources to change the sample rate of the incoming audio signal. Otherwise check out these various project paths….

1. Feature film – double system at 24fps and 48kHz audio recording for 24fps postproduction.
2. Film-based television providing sync dailies on DigiBeta (23.976 and 48kHz) for 23.976
3. Film or HD Production at 23.976 with single or double system audio recording for 23.976
4. Feature film and film-based television production at 24fps with hard disk recording at 48.048kHz for 23.976 postproduction.

1. Feature Film Double System

Most, if not all, feature film production intended for theatrical shoots film at 24fps while recording audio digitally at 48kHz. the film is now running at 23.976fps during the telecine process in order to create a known 2:3 pulldown cadence to the 29.97fps video rate. Once digitized into a 24p project, the frames are “stamped” as 24fps in order to play back in sync with audio captured directly via AES/EBU or Broadcast WAV files recorded at 48kHz. Because the audio was captured digitally – either synced to work clock or imported as 48kHz – it expects to be in sync with the picture as it was originally captured – 24fps. The native sample rate of a 24p project is 48kHz and all other rates are resolved to that during capture. When playing back at 48kHz, the audio plays back .1% faster creating a true 24fps playback from 23.976 sync sources. When capturing digitally at 48kHz, no samples are converted. It is a digital clone.

2. Film-Based Television with Sync Dailies
The transfer facility has already resolved the original shooting rate of 24fps to 23.976 and has sample-rate-converted the digital audio sources to be in sync in the digital source tapes. the audio must be sample rate converted when going from 24fps to 23.976 on the video. The path looks like this: Picture: 24 -> 23.976 to 29.97 video creating 2:3 pulldown Audio: 48kHz -> 47.952 slow down (.1%) sample corrected -> 48kHz to 29.97 video. If the editors are cutting in a 30i project (29.97 NTSC video), the audio sample rate is unchanged when capturing – it is a digital clone.

If it’s decided that postproduction will work in a 24p project, the digitized samples are slowed to bring everything back to a true 24fps = 48kHz environment.
In this case, the postproduction should be done in a 23.976 project type, since it assumes that the 48kHz audio sample rate is in sync with picture playing back at 23.976fps from the DigiBeta captured sources. It has the same result than that of a film-to-tape transfer to tape. But since there is no need to speed up to true 24fps in this project, audio samples remain untouched at 48Khz throughout the postproduction process, through the audio mix and back to the NTSC broadcast master. Using this project type for this workflow will only go through one sample rate conversion during the film to tape transfer.

3. Film or HD Production at 23.976
shooting rate is 23.976fps because of the audio consideration when down converting to NTSC. No one wanted to deal with a sample rate conversion in the audio when working in a fully digital environment. In a double system environment, the DAT or hard disc recorder records at 48kHz. So shooting at 23.976fps eliminates the need to do a sample rate conversion. The resulting NTSC down convert is now the same as in the previous example where 23.976 video with 2:3 pulldown is in a Digital tape with sync 48kHz audio.
If working double system, the DAT or BWF files from the hard disk recorder, the 48kHz recording will come straight in with no sample rate conversion or speed change to sync with the 23.976 picture.

4. Feature Film with 48.048kHz Audio Recording
audio workflow at 23.976 with the film running at 24fps. This workflow is only for picture capture frame rate of true 24fps and a NTSC postproduction workflow. DAT, and more common to this workflow, hard disk recorders, can record at 48.048 kHz – which is really just 48kHz with a .1% speed up as part of the capture.

Film/24p Settings
editing systems with 23.976 project types support a 48.048kHz BWF import workflow. If no sample rate conversion is chosen, the imported files are stamped as 48kHz, thus slowing them down by .1%; the same amount that the film is slowed down during the film to tape transfer. This way no sample rate conversion is performed, and a digital audio pipeline is maintained for the postproduction process.

Capture, Edit, Digital Cut
Capture: The project type determines the native capture rate of the project, either 23.976 or 24p. It also determines the native audio sample rate of that project that will not have a sample rate conversion or analog process involved when capturing, playing, or digital cut.

Edit: In the Film/24p settings you will see the “Edit Play Rate” as either 23.976 or 24. This control sets the play rate of the timeline. It does not affect any of the digital cut output settings. This control lets you set a default state of frame rate for outputs that are made directly to tape, such as a crash record.

Digital Cut: Here you can output the timeline as 23.976, 24, or 29.97. The important thing to remember is that this is the playback speed of the Avid timeline, not the source tape destination. The NTSC frame rate of 29.97 cannot be changed. What is changing is the frame rate of the picture within the NTSC signal.

1. 23.976. This creates a continuous 2:3 cadence from beginning to end of a sequence and is the expected frame rate of a broadcast NTSC master from 24 frame sources.

2. 24: This is used for feature film production to create a true “film projected” speed from an Avid timeline on NTSC video. It is also the output type to use when using picture reference in a Digidesign Pro Tools system using OMF media from a 24p project type. Note that this is not a continuous 2:3 cadence. Adjustments are made over 1000 frames with the pulldown cadence. No frames are dropped, just the field ordering with the 2:3 cadence.

3. 29.97: Timeline will play back 25% faster to create a 1:1 film frame to video frame relationship. This can be considered a 2:2:2:2 pulldown cadence. This
output is useful for animation workflow or low cost kinescope transfers where a 2:3 pulldown cannot be properly handled

Convert 60i to 24P
Use this option for standard interlaced NTSC shot at 1/60th sec shutter speed, where you wish to edit at 24P for the purpose of transfer to film or to author a 24P DVD. If this option is selected, all film effects (widescreen, grain, red boost) will be disabled. These effects can be added after editing.

Convert 3:2 Pulldown to 24P
Use this option for NTSC which was shot in 24P normal mode with a standard 3:2 pulldown, or with video that originated on 24 frames/sec film, where you wish to edit at 24P for the purpose of transfer to film or to author a 24P DVD. If this option is selected, all film effects (widescreen, grain, red boost) will be disabled. These effects can be added after editing.

Convert 2:3:3:2 pulldown to 24P
Use this option for NTSC video that was shot in 24P with a 2:3:3:2 pulldown, or 24P-NTSC archival material created with a 2:3:3:2 pulldown. Convert 2:3:3:2 Pulldown to 24P is the only option that works without recompression of the video data.

Output 23.976 (23.98 )
Use this option to output 23.976 frames/sec Quicktime with 48000 Hz audio, instead of 24.000 frames/sec Quicktime and 48048 Audio. This option works best with editing programs that can set the timeline to exactly 23.976 frames/sec. If this option is not used, then the Quicktime’s playback rate is 24.000 fps and the audio playback rate is set to 48048 Hz to keep perfect sync, and the 24.000 frames/sec timeline must be set up for 48048 Hz audio.

So find out exactly what path the production team used and find out how i was edited and finally what speed/frame rate they want you to work in and to deliver to.