[MPlayer-users] a/v sync problem

Heitzso heitzso at growthmodels.com
Tue May 31 15:51:10 CEST 2005

I am working on a project with 55 DV tapes, roughly
half of which originated (I believe) with a Canon camera
with the 48009 constant audio bit rate problem.
What that means is if you view the DV file straight
the A/V sync is fine.  But if you split out the A/V streams,
compress, and join them back together you end up
with a slowly increasing A/V sync problem that starts
to be noticable after 15 or 20 minutes.

I'm having an incredibly difficult time trying to compress
these broken files because most tools assume the audio
is to spec and is 48000.   And they won't let you override
the spec 48000 with 48008.

I've managed to split out the audio stream using ffmpeg
to a wav file, then use ecasound -ei to alter the length of
the file, but ecasound's -ei parameter doesn't hold enough
precision for the very small (but absolutely critical)
adjustment I need ( -ei 100.018141% ).

I don't know how to resample between 48009 and 48000
because the audio file split out from the DV file claims it
is 48000 already.

I would GREATLY appreciate help.  This is beating me
to a pulp. 

For a reference see
/"This was revealed at NAB '99 by Randy Ubillos, lead engineer on Final 
Cut Pro, who has found that while most DV cameras are pretty good, Canon 
cameras grab 48kHz sound at around 48.009 kHz, which can result in 
almost a second of video/audio slippage over the course of an hour (or 
around one frame every two minutes)."


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