[MPlayer-users] a/v sync problem

Giacomo Comes comes at naic.edu
Tue May 31 16:34:04 CEST 2005

On Tue, May 31, 2005 at 09:51:10AM -0400, Heitzso wrote:
> 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.

If you use mencoder to encode the video, adding the option 
-srate 48000 should solve the problem. Have you tryed it?
(use it togheter with -af-adv force=1 and, may be, -af resample)


> 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
> http://www.adamwilt.com/DV-FAQ-tech.html#LockedAudio
> /"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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