[Matroska-devel] audio async when muxing MP4 files into MKV with mkvtoolnix 2.0.2

Moritz Bunkus m.bunkus at linet-services.de
Mon Feb 26 10:57:42 CET 2007


Hey,

On Saturday 24 February 2007 23:05, Christian HJ Wiesner wrote:

> i am converting MPEG captures from satellite into MP4 files, using VLC
> 0.86a. Both the MPEG and the MP4 file are perfectly in sync. However,
> the final MKV, after being muxed from the MP4 with latest mkvtoolnix,
> will be async. I am not setting any time delays for the audio track, so
> i wonder why this is ?
>
> The delay i have to use to get it into sync is between -200 to -1400 ms
> for the audio track, meaning the audio is normally too late after
> muxing.

I think that the MP4 demuxer in mkvmerge does not handle audio which
does not start at timecode 0 correctly (meaning the initial delay gets
lost). Could you upload a test file for me please?

> Here the warning that mmg is giving me during muxing :
>
> ''CTTS' atom is needed for getting the timecodes right. As it is missing
> the timecodes for this track might be wrong. You should watch the
> resulting file and make sure that it looks like you expected it to.'

This is only a problem if the video track contains B frames. If it does
then the video might stutter. But it has nothing to do with your audio
delay problem.

Mosu

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