Converting 23.976 to 25fps [WAS: Re: [MPlayer-users] 3:2 pulldown]

Martin Emrich martin at
Sat Jan 10 22:22:24 CET 2004


Am Fr, den 09.01.2004 schrieb Martin Emrich um 17:20:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hi!
> Am Mi, den 07.01.2004 schrieb Martin Emrich um 00:51:

> > Done. Hacked the AVI to 25fps. Sox will hopefully take care of the audio.
> I made the audio (25/23.976) times faster (this went correct, as
> (audiolength_before/audiolength_after) == (25/23.976)) and muxed the
> audio file back into the hacked avi with "-oac copy -ovc copy -audiofile
> audio-25.wav". But all I get is terrible audio desync. That much for a

Today, I started all over again:

Took the original AVI, recoded it to very-high-bitrate MPEG4 with PCM
audio (Hacking the audio sample rate on the origial with MP3 audio didnt
work), plays fine, with no visible quality loss.

Then I hacked the header to an audio sample rate of 45983Hz
(44100*(25/23.976)). (I hacked the videe frame time to 0.0400sec =
0x9c40, too, but mplayer didn't care, uses still 23.976fps; wonder where
it gets this number from...). 

So I thought it should play fine now with "mplayer -fps 25". But I got
the audio desync again. So I experimented with -fps, and found out that
if I use -fps 27.40 (!), it plays almost correct (by watching lip sync
at ca. 60sec playing time). I tried with and without -af resample=48000,
to rule out issues with the sound card driver (SB Live+Alsa), and with
and without "-ni". I wonder where this weird framerate of 27.4fps comes
from. Ideas?



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