[Nottingham] mp4 playback audio slippage (loss of sync)

Martin martin at ml1.co.uk
Tue Sep 11 18:51:46 UTC 2012


As demonstrated at the last meetup...

I've bolted together various mp4 files using:

cat file??.mp4 >video.mp4

where I've a long list of video snippets files file00.mp4,
file01.mp4,... All encoded as MPEG transport stream TS... (OK, so not
completely free as in freedom, but with limited available time to bolt
things together...)

That works fine and there's no visible glitches for the video editing
(using Avidemux), but... The audio loses sync at each file join and
incrementally gets progressively worse as you run over each concatenated


What's a better way of doing that so as to keep the audio in sync with
the video?

Or have I just tripped over problems due to using VBR rather than CBR?...

This is all to be fixed for a future showing of the fun second half of
the virtuality talk/demo/video. (The 'how' and 'Wow!' have been covered.
The second half is about the infiltration into the real world and how
most people are scarily unaware...)

Ideas welcomed,


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