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Exporting H264 with TC Ref for mix is not frame accurate
Hello fellow cows,
I’ve done some googling and have not been able to pinpoint this specific problem.When I export a reference video for my audio mixer to use as a frame accurate, with timecode burned in (no offest or anything out of the ordinary), and a 2 pop/beep, the resulting video is not frame accurate.
Example: I ahve a ProRes 4444 timeline and assets. 29.97, 1920×1080, non drop timecode, 48/24 audio. My countdown and 2 beep is exact, the 2 and beep is right on 00:59:58:00, and program starts on the hour. I usually give the full 10 second countdown, but in this case it doesn’t matter, but I always give at the very least a 2 beep with the video. I export a Quicktime .mov H.264, smaller resolution, same framerate, same audio setting (48 khz) etc. The resulting video that gets spit out always has about a 2/3 of a frame of silence before the 2 beep, which then sets everything off down the line by 2/3 of a frame. The TC ref on the video still says 00:59:58:00 though, and when I bring it in to line up with the ProRes 4444 timeline, you can see the offset. My audio mixer (in ProTools) has found that it’s about a 513 sample difference.
Why is this? It’s only when I’m encoding to a compressed codec like H264 (either .mov or .mp4). it’s usually .mov for me since ProTools seems not to like .mp4. And when I do a test by exporting native codec prores 4444, it lines up perfectly, with no offset.
Is there a work around for this? Here is a screengrab of the 2 beeps so you can see the offset.
Thanks,
Joseph
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It appears that this is not discussed that widely, but I did find some threads of problems that have the same symptoms. Anyways, it’s the AAC encoding, and here’s the white paper about the encoder delay and synchronization. Hope this helps people out.
Technical Note TN2258: AAC Audio – Encoder Delay and Synchronization
work.tulpapictures.com
Twitter/Vimeo/Facebook: @TulpaPicturesMac Pro 2.4GHz 12 Core Intel Xeon (5,1) 32GB RAM
Macbook Pro 2.3 GHz Intel Core i7 (8,2) 4 GB RAM
OSX 10.8.5
Adobe CC
FCS3
Davinci Resolve
AJA Kona LHi/Blackmagic
MSI Twin Frozr GeForce GTX 680 4GB GPU
EVGA GeForce GT 640 4GB GUI
RocketRAID 4322 SAS
ProAvio 8TB RAID5 SAS
Own Cams: BMCC 2.5K EF, GH3, Hacked GH2, 5DMKII
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