Georgia Hilton MPE CAS MPSE Prod/Dir/Editor

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Film / Video post speed/frame rate issues...

Posted on February 28, 2010 at 1:05 AM

Film / Video post speed/frame rate issues... PLEASE:

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

4. DELIVERY SPEC!!!!

The first question to ask when dealing which projects: is the pictureframe rate in sync with 48kHz. If so there will be no need to do asample rate conversion or digitize via analog sources to change thesample rate of the incoming audio signal. Otherwise check out thesevarious 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

postproduction.

3. Film or HD Production at 23.976 with single or double system audio recording for 23.976

postproduction.

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 theatricalshoots film at 24fps while recording audio digitally at 48kHz. the filmis now running at 23.976fps during the telecine process in order tocreate a known 2:3 pulldown cadence to the 29.97fps video rate. Oncedigitized into a 24p project, the frames are “stamped” as 24fps inorder to play back in sync with audio captured directly via AES/EBU orBroadcast WAV files recorded at 48kHz. Because the audio was captureddigitally – either synced to work clock or imported as 48kHz – itexpects 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 otherrates are resolved to that during capture. When playing back at 48kHz,the audio plays back .1% faster creating a true 24fps playback from23.976 sync sources. When capturing digitally at 48kHz, no samples areconverted. It is a digital clone.

2. Film-Based Television with Sync Dailies

The transfer facility has already resolved the original shooting rateof 24fps to 23.976 and has sample-rate-converted the digital audiosources to be in sync in the digital source tapes. the audio must besample rate converted when going from 24fps to 23.976 on the video. Thepath looks like this: Picture: 24 -> 23.976 to 29.97 video creating2:3 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, thedigitized 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 projecttype, since it assumes that the 48kHz audio sample rate is in sync withpicture 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 postproductionprocess, through the audio mix and back to the NTSC broadcast master.Using this project type for this workflow will only go through onesample 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 downconverting to NTSC. No one wanted to deal with a sample rate conversionin the audio when working in a fully digital environment. In a doublesystem environment, the DAT or hard disc recorder records at 48kHz. Soshooting at 23.976fps eliminates the need to do a sample rateconversion. The resulting NTSC down convert is now the same as in theprevious example where 23.976 video with 2:3 pulldown is in a Digitaltape with sync 48kHz audio.

If working double system, the DAT or BWF files from the hard diskrecorder, the 48kHz recording will come straight in with no sample rateconversion 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 workflowis only for picture capture frame rate of true 24fps and a NTSCpostproduction workflow. DAT, and more common to this workflow, harddisk recorders, can record at 48.048 kHz – which is really just 48kHzwith a .1% speed up as part of the capture.

Film/24p Settings

editing systems with 23.976 project types support a 48.048kHz BWFimport workflow. If no sample rate conversion is chosen, the importedfiles are stamped as 48kHz, thus slowing them down by .1%; the sameamount that the film is slowed down during the film to tape transfer.This way no sample rate conversion is performed, and a digital audiopipeline is maintained for the postproduction process.

Capture, Edit, Digital Cut

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

Edit: In the Film/24p settings you will see the “Edit Play Rate” aseither 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 controllets you set a default state of frame rate for outputs that are madedirectly 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 ofthe Avid timeline, not the source tape destination. The NTSC frame rateof 29.97 cannot be changed. What is changing is the frame rate of thepicture within the NTSC signal.

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

2. 24: This is used for feature film production to create a true “filmprojected” speed from an Avid timeline on NTSC video. It is also theoutput type to use when using picture reference in a Digidesign ProTools system using OMF media from a 24p project type. Note that this isnot a continuous 2:3 cadence. Adjustments are made over 1000 frameswith the pulldown cadence. No frames are dropped, just the fieldordering with the 2:3 cadence.

3. 29.97: Timeline will play back 25% faster to create a 1:1 film frameto video frame relationship. This can be considered a 2:2:2:2 pulldowncadence. 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 shutterspeed, where you wish to edit at 24P for the purpose of transfer tofilm or to author a 24P DVD. If this option is selected, all filmeffects (widescreen, grain, red boost) will be disabled. These effectscan be added after editing.

Convert 3:2 Pulldown to 24P

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

Convert 2:3:3:2 pulldown to 24P

Use this option for NTSC video that was shot in 24P with a 2:3:3:2pulldown, or 24P-NTSC archival material created with a 2:3:3:2pulldown. Convert 2:3:3:2 Pulldown to 24P is the only option that workswithout recompression of the video data.

Output 23.976 (23.98 )

Use this option to output 23.976 frames/sec Quicktime with 48000 Hzaudio, instead of 24.000 frames/sec Quicktime and 48048 Audio. Thisoption works best with editing programs that can set the timeline toexactly 23.976 frames/sec. If this option is not used, then theQuicktime's playback rate is 24.000 fps and the audio playback rate isset to 48048 Hz to keep perfect sync, and the 24.000 frames/sectimeline must be set up for 48048 Hz audio.

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

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