DCP audio workflow from After Effects problem…

[Walter Soyka]

[Ty DesEnfants] “Is there a way to tell if the wav files are 24fps, or is that just a given since they are exported from a 24fps After Effects comp?”

Audio files don’t have a frame rate — after all, they have no frames. They do have a sample rate: 48 KHz audio has 48,000 samples per second.

Splitting your stereo WAVs is very simple in Adobe Audition:

• Import the WAV file you exported from After Effects.
• Edit > Convert Sample Type (Shift-T), then set it to 48000 Hz and 24 bits.
• Edit > Extract channels to mono files.
• File > Save all.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Ty Desenfants]

Thanks for your response.

That makes sense that a wav file does not have a frame rate, however, when the file is converted to DCP format an mxf file is created with the mono wav files and that does seem to have a frame count that corresponds with the frames of the picture.

Could it be that my frame count (length) is getting off in conversion? Should there be any difference at all in length between a 32bit wav and a 24bit wav?

Is there any way to do what you have described without Audition?

[Walter Soyka]

[Ty DesEnfants] “Could it be that my frame count (length) is getting off in conversion? Should there be any difference at all in length between a 32bit wav and a 24bit wav?”

Wait, I must have missed something. You have a sync problem?

There will be no difference in length between a 32b WAV and a 24b WAV. Audio bit depth is a somewhat like video color depth; it won’t affect the length and shouldn’t cause any sync drift.

[Ty DesEnfants] “Is there any way to do what you have described without Audition?”

Sorry, I missed that you were on CS4 the first time around. (Upgrade if you can — there are huge improvements in AE CS5 and CS6 that you’re missing out on.)

There’s a free, open source editor called Audacity that you could use.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog – What I’m thinking when my workstation’s thinking
Creative Cow Forum Host: Live & Stage Events

[Ht Davis]

Audio is done in samples. When you export the audio for use in DCP, however, there is usually metadata attached conforming the samples to a given frame rate when you attach it in AE or audition (an option tick box). If the audio is getting out of Sync with the picture, I would suspect you have another problem, but with your video, not the audio.

Cameras can have stabilizers or special algorithms to drop frames when motion or camera shake are detected that go beyond a certain limit. When this happens, you get what is called VARIABLE FRAME RATE video. DO NOT CONFUSE THIS WITH VBR (VARIABLE BIT RATE). Think of celluloid film… …Remember the old class projector? Good projectionists were very stable at around 24fps, but weren’t perfect. When auto projection came out, it as much better, but still not perfect. When better video technology pushed to 29-30fps, it was much smoother, and while some stuck with 24 frames, the technology allowed them to do it much more smoothly to give the memorable motion attributes from standard television in NTSC. 25 frames was used for PAL formats. With digital systems we have today, cameras have the ability to detect and reduce camera shake, to make the video “Feel” more natural and smooth, but it makes editing more difficult in professional applications. By dropping frames in a certain area, they throw off the sync. Most apps will work just fine playing it back on it’s own, but some will only play the available frames, and play them at the single set rate. I think OpenDCP is one of those last ones. By jumping over dropped frames, without changing the playback rate, they get out of sync with the audio.

The fix:
You have to use an encoder that allows you to force a CONSTANT FRAME RATE. The bit rate should be Variable. The FRAME RATE should be FORCED TO CONSTANT. Bit rate is data transmission and has nothing to do with the number of frames per second. Handbrake, AME, Compressor. Encode to a format that can force a constant frame rate. In adobe, look for a box that says “Frame Blending”. Export from AE with frame blending on, and it will force a constant rate, and fix the frames for you by BLENDING the surrounding frames to create new frames where the missing ones are.