Quote:
Originally Posted by justnobody
example one
a video from iTunes having -42ms in audio (almost every iTunes video has delay in audio, audio format is AAC, iTunes loves AAC), 23.976fps
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Maybe it is a delay from video re-ordering (bframes)? 1000/(24000/1001) ~= 41.7ms ~= 42ms
Or could be because of AAC encoder delay (though I expect 44ms, then. ~42.66.. ms is length of 2 AAC frames) . The most common lossy audio formats have this.
https://developer.apple.com/library/...TFFAppenG.html
Now whether or not this is really stored correctly in your original file ... no idea. ~40ms is hard to tell confidently.
Quote:
Originally Posted by justnobody
I cut a small piece out of it (mkvtoolnix), delay is now 5ms
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This is misleading because video and audio frames have different lengths and they won't 100% align at the cut point. Mkvmerge stores delay via container to make up for this.
Quote:
Originally Posted by justnobody
and we demux this file with eac3to and put them (all tracks) together again with mkvtoolnix, delay is gone, 0ms now
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If you demux to "raw" (ADTS) AAC there is no way to store the delay infos that mkv or mp4 container can store. It is lost. You will introduce a slight delay (here: -5ms). MediaInfo doesn't know this. It is not an AI that analyzes e.g. speech to mouth movement of video but only looks at the delay values stored in the container (mkv/mp4).