[MPlayer-users] Re: 3pass audio sync problem
Jonathan Rogers
jonner at teegra.net
Sun Jun 29 13:25:20 CEST 2003
Renai wrote:
> When I encode files with 2 pass encoding, using the following commands, I
> don't have the same problem.
>
> mencoder -o /dev/null -ovc lavc -lavcopts vcodec=mpeg4:vhq:aspect=4/3:vpass=1
> -vop lavcdeint -oac copy stream.dump
>
> mencoder -o divx.avi -ovc lavc -lavcopts vcodec=mpeg4:vhq:aspect=4/3:vpass=2
> -vop lavcdeint -oac copy stream.dump
>
> Can anyone enlighten me as to what I am doing wrong here, or is this a
> limitation of mplayer?
I think you've already solved the problem: just don't use the frameno
thingy. I really don't know what it's useful for or how it's supposed to
work. I've asked about it on mailing lists, but never gotten a straight
answer. Also, it's always a good idea to specify "-ofps", at least for
NTSC input. In particular, it's necessary if you are encoding film that
has been telecined. If you don't have NTSC DVDs, you probably have no
appreciation for what we have to deal with here in the US (count your
blessings).
Is it that you want to reencode audio instead of copying the audio
stream from the original? You can just use "-oac pcm" for the first pass
and "-oac mp3lame" for the second. Of course, you probably want to know
what video bitrate to use beforehand in order to fit the final video
into a certain size. You can know how big audio will be if you use CBR,
but that won't give the best quality.
You can encode the audio as a first step to find out how big it will be.
Then, encode the two video passes using "-oac pcm", discarding the
output from the first pass. I've been told that sync could be lost if
you don't decode audio while encoding video. Finally, remultiplex the
audio and video into the final target.
I haven't tried this procedure with AVI, since I prefer to use Vorbis
audio, which doesn't work well in AVI. I use either ogmmerge or mkvmerge
to produce a final OGM or Matroska file. Read the encoding-tips.txt file
in the DOCS directory. If you have MP3 audio and AVI video, you should
be able to multiplex them into a final AVI using mencoder with the
"-audiofile" option. I've heard bad things about VBR audio in AVIs,
though, so you may want to use OGM or Matroska anyway, even if the audio
is MP3.
Jonathan Rogers
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