avconv gives audio and video out of sync

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avconv gives audio and video out of sync

Postby hgeorg » 2015-09-10 08:45


I have a problem with avconv. Most of the use cases work spledidly, but when I need to crop a segment and then splice multiple segments together, I get problems.

The process I use is this
1. Raw recording of short segments in high-quality AVI, These are produced by avconv, some as screencast and some by combining a PNG file with flac audio from audacity.
2. Conversion segment by segment into mp4 and ogv
Options A: -acodec aac -strict experimental -ab 128k -ac 2 -vcodec libx264 -s 640x480 -pix_fmt yuv420p -movflags +faststart -crf 22
Options B: -acodec libvorbis -ab 128k -ac 2 -vcodec libtheora -s 640x480 -b 500k
3. Splicing of the segments using MP4Box or oggCat.
(I used to do this in ffmpeg, but I have not figured out how to do it in avconv.)
This works.

In some cases I need to crop the segments, using the copy codecs and the -ss and/or =t options.
If I crop the AVI segments (between 1 and 2) the sound is clipping (this also generates a spree of error
messages `Non-monotonous DTS'). If I crop mp4/ogv segments, (between 2 and 3) the remaining video,
after the cropped segment are out of sync. I get the same problems with both OGV and MP4 playing them in
vlc. Playing the mp4 directly in iceweasel works as it should.

Does anyone have any idea what is going on? Is there a way to resolve it?

:-- George
Posts: 31
Joined: 2013-08-27 22:29

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