[Ffmpeg-devel] closed captioning bug?

Luca Abeni lucabe72
Sat Apr 22 10:41:36 CEST 2006

On Sat, 22 Apr 2006 02:51:19 -0400
Cyrus A <lists at rooseveltmedia.com> wrote:
> > ok, ive not the faintest idea whats wrong but does chaning the
> > resolution / encoding to /dev/null using -vcodec copy help?
> >
> > btw, are there any distortions in the video vissible?
> > maybe the diskaccess for encoding is causing some buffers of the
> > capture hw to overrun in that case hdparm / pci settings
> > might have some effect
> >
> > [...]
> >
> >   
> I think it's ALSA. I just tried ffmpeg with "-an" and captions work 
> fine.
I had similar problems in the past, and I do not think the cause is alsa. In my opinion, it is the A/V synch code in ffmpeg.c that does not work well with video4linux + oss input.

I think you have 2 possibilities:
1) go in ffmpeg.c:do_video_out(); about 10 or 20 from the beginning of the function you see something like 
if (vdelta < 1.1) 
else if (vdelta > 1.1)
Change 1.1 with something bigger (around 5 should be enough, if I remember well), and it should fix your problem.
This is clearly a hack :)

2) the correct solution: use v4l2. Which brings the question: why is it not used? I suspect there is a problem in the check in configure (which might be too conservative, to avoid breaking the build).
You are using fedora, right? I might have a patch somewhere that could help... I'll search for it, and I'll send it later.


More information about the ffmpeg-devel mailing list