[MPlayer-users] SkipFrame/Duplicate Frame

[Tim U.]

On Wed, Feb 13, 2002 at 02:36:02PM -0800, Charles Henrich wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> > > Skip frame messeges mean that mencoder has dropped a frame, either to keep
> > > the he audio syncronized or because of a 3:2 pull down removal.  If this
> > > is true is
> > it shouldn't happen for pulldown if user specified the exact -ofps
> 
> No matter what fps I specify for this DVD it always comes up with some skip
> frame and duplicate frame messages.
> 
> > > there a way to tell mencoder to encode every frame regardless of the audio
> > > sync?  
> > yes. -mc 0
> 
> Even with -mc 0 I see "skip frame" messages?

Same here.

> > > Duplicate frame messages on the other hand are information meaning
> > > mencoder found a duplicate frame, but is happily encoding it (whhich would
> > > show up as jerky pans in the video).
> > nope. it means mencoder duplicated a frame to keep a-v sync or requested
> > -ofps
> 
> Is there anyway to force mencoder to not duplicate frames?  Aka "look encoder,
> I want an exact frame for frame copy of this source material?"
> 
> > > How does mencoder actually do the removal, is it smart enough about the
> > > field d encoding to remove the appropriate fields, or does it just whack a
> > > whole frame?  (How does this work with deinterlace post processing?)
> > whole frame. it works for pulldown
> 
> Perhaps this is the trouble Im having with these streams that no matter what
> -ofps I select I get a mixture of skip/duplicate frames.
> 
> The only real way to do proper 3:2 pulldown removal is to compare fields
> against one another, and remove the duplicate field.  I.e. the stream will
> contain something like:
> 
> Original Speed      F1 F2 F3 F4   (Frame 1-4)
>     
> Field 1             F1 F2 F2 F3 F4
> Field 2             F1 F2 F3 F4 F4
> 
> The pattern is not guranteed, and varies by different encoder unfortunatly!
> The simple solution is to keep a running count of fields, and whenever a field
> occurs three times, skip the third field.  Which would give you the correct
> output rate (calculated) as well as a perfect progressive playback.

As I've learned (and been told), most DVDs (that I've seen) don't 
require a 3:2 pulldown, since they have only 24 FPS of hard-coded 
frames, and the field duplication is done by the decoder.  MPlayer 
doesn't do the field duplication, so no 3:2 pulldown is necessary.

At least that is the case for most DVDs, in my experience.  But some 
DVDs have hard-coded 29.97 FPS sequences (with noticeable telecine 
artifacts) mixed right in with the 24 FPS sequences.

I posted a message in January about this (I probably should have 
posted it to -users).  You can view it here:

http://www.MPlayerHQ.hu/pipermail/mplayer-dev-eng/2002-January/004502.html

And here is another message, this time I included a couple screen 
captures of mplayer:

http://www.MPlayerHQ.hu/pipermail/mplayer-users/2002-January/010163.html

  - Tim