[MPlayer-users] frames skipped when grabbing DVD

[Daniel Dawson]

On Thu, Jun 24, 2010 at 07:22:59PM +0200, Matus UHLAR - fantomas wrote:
> On 10.06.10 17:02, Daniel Dawson wrote:
> > DVD-Video can be 23.976 fps or one of 25 fps or 29.97 fps (depending on
> > the television format). Some video streams switch framerates in the
> > middle (e.g. a 24 fps film with bits of video mixed in).
> 
> can I detect this somehow in mplayer/mencoder?

Well, it does print notices about such switching in the terminal under
default verbosity settings, though you may not see it with all the
"Skipping frame!" or "1 duplicate frame(s)!" messages scrolling the
terminal. You can turn off those messages by setting -msglevel
mencoder=1 (or lower). Supposedly the framerate notices will leave the
position of the last frame of the previous rate showing, though I'm not
sure if it's frame-accurate, and the numbering gets confusing when
switching framerates. If you can work it out, you could transmux
different sections to separate files and put them together into a
Matroska file or something, though that could be tedious and might have
hidden problems.

Actually, it's likely the stream is really all 23.976 fps, in which case
it's pretty simple: try overriding the framerate with the -fps option
(after you verify it really is a single framerate, of course, or else
you'll get weird artifacts on the video-framerate parts).

> > I'd go with Alexander's suggestion. Use mplayer to dump the VOB.
> > 
> > Of course ideally, mencoder would support muxing VFR streams, but...
> 
> where does this problem lie, in formats or in mencoder itself?

Well, the popular container format AVI doesn't support VFR, which is
becoming more and more common these days (not just on DVDs anymore). But
AVI is pretty old. There are much better formats, like the
aforementioned Matroska. ffmpeg, mencoder, etc., prefer encoding to AVI,
and perhaps because they're designed around AVI, they don't support
encoding (or muxing) VFR. Some of the other container formats supported,
like e.g. MPEG-2 and MPEG-4, do support VFR more or less, but these
programs don't support encoding it.

So I would have to say the problem lies mostly with the ffmpeg family. I
can't really hold it against them too much, though.

Anyway, it's easiest to either dump the VOB stream with -dumpstream (I
think you need to pick your video, audio, and subtitle streams when you
do this; it won't dump them all), or transcode it.

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