[MPlayer-users] Re: Question on "trans-coding" with mencoder...

[D Richard Felker III]

On Wed, Aug 20, 2003 at 07:40:55AM +0200, Rainer Hantsch wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hi!
> 
> I let a conversion run over night as you recommended:
> 
> 1.  Concatenating both parts into one big mpg file
>     cat part1.mpg part2.mpg > complete.mpg
> 
> 2.  Extracting the audio track as-is (because it is already MP3):
>     mencoder complete.mpg -ovc frameno -oac copy -o frameno.avi
> 
> 3.  Doing the first pass of video conversion:
>     mencoder $ori -oac copy -ovc lavc \
>     -lavcopts vcodec=mpeg4:vpass=1:vbitrate=2100 \
>     -o /dev/null -vop scale=720:540 -sws 2
> 
> 4.  Doing the second pass of video conversion:
>     mencoder $ori -oac copy -ovc lavc \
>     -lavcopts vcodec=mpeg4:vpass=2:vbitrate=2100 \
>     -o final.avi -vop scale=720:540 -sws 2
> 
> 
> What I got is an AVI file which can be played with gmplayer only with option
> -idx (otherwise I cannot skip scenes), while XINE can skip forward/backward
> without problems.
> 
> But as I experienced with other similar done conversions too, it happens
> with some files that synchronization is lost when the point of concatenation
> is reached.
> 
> Is the above procedure (about how I convert) correct, or should I do something
> different?

AVI files greater than 4 GB (or is it 2?) are not seekable. With such
an insanely high bitrate (2100 for video), I would expect you're going
over that limit. Read encoding-tips.txt for info on how to make a good
encode with reasonable size. At the very least, you NEED -lavcopts
vhq, and you probably need to crop too. Scaling vertically up to 540
is also a bad idea; you'd be better off scaling down horizontal to
640, or just storing the aspect in the header (-lavcopts
[auto]aspect).

As for A/V sync, I would recommend NOT doing pass0 (the audio
prepass). It's buggy, and maybe even moreso with concatenated files
and/or -oac copy. There's no use whatsoever for it anyway, since
you're just copying the audio. So if you try again, delete frameno.avi
and skip that step.

Rich