[MEncoder-users] mkv to hard sub avi to m4v command line options and sync problems

[Reimar Döffinger]

On Sun, Jan 17, 2010 at 07:55:06AM -0600, James Hastings-Trew wrote:
> Reimar Döffinger wrote:
> >On Sun, Jan 17, 2010 at 07:17:06AM -0600, James Hastings-Trew wrote:
> >>v4r4n wrote:
> >>>$> mencoder -oac copy -ovc raw -sub subtitles.srt -sub-bg-alpha 255 -utf8 -o
> >>>output.srt.avi input.avi
> >>>
> >>>to make a large raw with baked subtitles, then Handbrake to re-encode that
> >>>into an iPod .m4v file.  This works well enough, but the original visual
> >>>artifacts that I saw in the raw are still there.
> >>I'm not sure how you could expect it to be otherwise. That command
> >>line leads me to believe the artifacts are part of the original .mkv
> >>file, since raw would not add any artifacts of it's own.
> >
> >Wrong, it will introduce decoding errors if you do not use -noskip.
> Are you saying that it will skip decoding frames, not just skip
> storing them?

?? No idea what you mean.
I mean it will skip storing the encoded data belong to whatever
frame it decides to drop, and that frame may have been referenced
by later encoded frames which is does copy - this breaks decoding
of those frames.
So with -ovc raw and an encoded format a skipped frame (as can happen
when you do not use -noskip) can mean there is one frame missing in
the resulting frame and there are possible another several 100
that are there bug can not be decoded correctly.
For those that can not be decoded correctly, FFmpeg uses error-concealment
and since that is quite good you usually see it only as the output
looking blocky, blurry or otherwise low quality.
The error-concealment can be tuned with -lavdopts ec=...  but it seems
it can't be disabled...