[MPlayer-users] composite input a/v sync issue

[Reimar Döffinger]

On Thu, Nov 05, 2009 at 05:50:08PM +0100, Miroslav Rovis wrote:
> 
> >> mencoder -fps 25 -ofps 25 -noskip -mc 0 -vf harddup,softskip tv:// -tv
> >> input=1:driver=v4l2:device=/dev/video0:normid=3:input=1:alsa:adevice=hw.0:audiorate=48000:amode=1:width=768:height=576
> >> -ovc lavc -lavcopts vcodec=mpeg4:autoaspect:vbitrate=8000 -oac mp3lame
> >> -srate 48000 -lameopts cbr:preset=standard -endpos 100  -o VHS155_`date
> >> +%H%M%S`.avi
> >>     
> >
> > While I do not know if it can even work without, -fps 25 tells
> > MPlayer/mencoder to assume that there are always exactly 25 frames per
> > second. If the capture card loses sync during the bad sections and does
> > not produce any frames that is of course not going to work out at all.
> >
> >   
> Thanks for trying to help. 25 frames per second is the PAL standard,
> it's by the book and by the google that anyone, as far as I had searched
> earlier, capturing PAL VHS on composite input do (some even recommend
> -fps 50)...

No, you misunderstand: -fps 25 tells MPlayer to assume the input to be
_exactly_ 25 fps no matter what, ignoring completely when the data arrives
from the capture card.
If you have a broken part in the video, it will not be able to capture _any_
frames, so during that time it is actually 0 fps, and with -fps 25 you explicitly
_forbid_ MPlayer to correct this.
There is also a fps option for -tv which is something else and which is supposed
to work in a saner way.
Still, to handle it properly you'd need support for variable frame-rate in-/output
which MPlayer does not have.