Date: Thu, 9 Jan 2003 19:22:47 +0100 From: Steve O'Hara-Smith <steve@sohara.org> To: Andre Albsmeier <andre.albsmeier@siemens.com> Cc: freebsd-multimedia@FreeBSD.ORG Subject: AV sync on ffmpeg captures - was Re: FreeBSD 4.7R: no sound when recording with ffmpeg? Message-ID: <20030109192247.0602e203.steve@sohara.org> In-Reply-To: <20030109144913.A30175@curry.mchp.siemens.de> References: <20021028202230.1283e8cd.steve@sohara.org> <Pine.BSF.4.21.0210292118440.11617-100000@brain.stagecraft.cx> <20021029194220.7fb532ad.steve@sohara.org> <20030106115851.A12349@curry.mchp.siemens.de> <20030106215821.60130d42.steve@sohara.org> <20030107085526.A14263@curry.mchp.siemens.de> <20030107191359.12abeb78.steve@sohara.org> <20030109144913.A30175@curry.mchp.siemens.de>
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On Thu, 9 Jan 2003 14:49:13 +0100
Andre Albsmeier <andre.albsmeier@siemens.com> wrote:
AA> On Tue, 07-Jan-2003 at 19:13:59 +0100, Steve O'Hara-Smith wrote:
AA> > On Tue, 7 Jan 2003 08:55:26 +0100
AA> > Please do, it would be good to confirm that the problem is not in
AA> > mplayer (I suspect it isn't but confirmation is good and I have no
AA> > windows).
AA>
AA> Hmm, tried the file in question with "Zoom Player" under Win32 and
AA> here the sync is perfect! So far so good, now one would say this is an
AA> mplayer problem. But there are two things left:
AA>
AA> 1.) I played lot of other mpegs using mplayer and the audio sync is
AA> ok.
Yep - I've played a lot of VOBs and AVIs in mplayer without sync
problems too. Timestamping in streams is an amazingly complex thing (ie.
I haven't managed to grok it yet). There are AFAICT multiple ways to work
out when things should be played, there is probably a consistency problem
in the streams generated by ffmpeg.
What this tells me is that I shouldn't try and fix this in the grab
code which is probably behaving well now, it needs fixing in the ffmpeg
stream building code (somewhere) which I don't understand properly (the
last time I tried to fiddle with it strange and unexpected things
happened, I retreated in confusion). It may be better in ffmpeg 0.46
unfortunately the performance of 0.46 leaves much to be desired - my XP
can't quite keep up with half resolution recording under 0.46 :(.
AA> 2.) When I use Virtualdub (which also runs under Win32 and has nothing
AA> to
AA> do with mplayer)
It probably digs out the timing in the same way as mplayer. What
happens if you just play back the stream with mplayer -fps 25.045 (or
perhaps about 24.95) ?
Can anyone point me to a comprehensible description of how the
timestamping is supposed to work in mpeg and avi streams ? If I can grok
what is supposed to be going on I can take a crack at fixing it.
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