Audio out of sync on MP4 Renders
A number of users have experienced audio sub-frame slippage when exporting MP4 files. When comparing two files, MOV and MP4, the waveforms will be ½ a frame off (500-ish samples). My bet is an offset needs to be added during the mixing process.
Ben Hickson commented
Has this been fixed? is there a quick way to offset my audio by 576 samples? i use mp4s as reference videos
This looks like an issue with AAC priming. A number of samples of silence are typically added at the beginning of the audio stream, to work around the fact that that signal reproduction in that region is very poor. The correct number of samples has to be trimmed on decode for audio to sync.
Nearly all AAC encoded MP4-files use 2112 samples for historical reasons.
The files created by Premiere seem to use a priming of around 1536 samples, which creates an offset of 2112-1536=576 samples (since most decoders assume 2112).
I have attached screenshot diagrams of this problem at the links below:
ht tps ://ibb . co / cHMmHz
ht tps ://ibb . co / ivJYxz
(Remove the spaces. Adobe - Shame on you for not allowing non-thread authors to post image attachments!)
I too have experienced this. I can provide screenshots, it happens every time. When exporting the MP4 (haven't tested the other formats), the audio track drifts forward on the newly rendered file. This is easy to see if you stack the RAW on top of the Premiere Rendered footage.
In addition to this, it also chops off a part of the audio at the end of the render!!
Adobe, this is unacceptable. Please fix!
Bryan Colvin commented
Also I tested with resolve 15 beta. Another person reported back that resolve 14.3 did not chop the first frame and did habe audio drift. Seemingly mp4 h264 codec is throwing devs for a loop!
Bryan Colvin commented
Yes it seems to only be when using compressed audio codecs like AAC. And I think Kyle meant "muxing" not mixing. **** auto correct! I did a test converting an mxf op1a to mp4 using AME and resolve. BOTH chop off the first frame, but AME export is shifting the audio sync. Resolve also chopped the first frame but kept audio sync in tact. Main gripe is the drifting audio, confiming approx 500 samples off, but a 2ndary gripe is it cutting off the first frame. I don't use mp4s for reference files but somepeople do, and that effectively shifts the timecode by one frame unless you do a proper timecode burn in to truly reference. Until this gets resolved I have to resort to resolve lol.