[Ffmpeg-devel] [PATCH]: A/V sync on nsv streams.

[Michael Niedermayer]

Hi

On Fri, Oct 27, 2006 at 01:18:47PM +0200, elupus wrote:
> Michael Niedermayer <michaelni <at> gmx.at> writes:
> 
> > 
> > Hi
> > 
> > On Fri, Oct 27, 2006 at 03:18:54AM +0200, elupus wrote:
> > > The current nsv demuxer in ffmpeg doesn't handle discontinuous nsv
> streams
> > > very well. This is streams that might send a commercial before the
> actual
> > > program. When the stream switches the video is garbled and a/v desync
> > > occurs. 
> > > 
> > [...]
> > 
> > >  <at>  <at>  -637,7 +638,14  <at>  <at> 
> > >          }
> > >          av_get_packet(pb, pkt, asize);
> > >          pkt->stream_index = st[NSV_ST_AUDIO]->index;//NSV_ST_AUDIO;
> > > -        //pkt->dts = nst->frame_offset;
> > > +        if( nsv->state == NSV_HAS_READ_NSVS ) { /* on a nsvs frame we
> have new information on a/v sync */
> > > +            pkt->dts =
> av_rescale(((NSVStream*)st[NSV_ST_VIDEO]->priv_data)->frame_offset-1, 
> > > +                                  st[NSV_ST_AUDIO]->time_base.den *
> st[NSV_ST_VIDEO]->time_base.num,
> > > +                                  st[NSV_ST_AUDIO]->time_base.num *
> st[NSV_ST_VIDEO]->time_base.den);
> > > +            pkt->dts += av_rescale(nsv->avsync, 
> > > +                                   st[NSV_ST_AUDIO]->time_base.den * 1,
> 
> > > +                                   st[NSV_ST_AUDIO]->time_base.num *
> 1000);          
> > 
> > rescaling timestamps is unacceptable set the timebase correctly with
> > av_set_pts_info()
> > 
> 
> Okey, but should I then set the timebase to be the same timebase as video,
> or to be in millisecond. The A/V correction is given in how many ms ahead of
> the video the audio is. While the video is set to a standard fps. The audio
> currently has a timebase of 1/samplespersecond, wich somewhat makes sence
> (even thou it can only be directly used for pcm data currently).
> 
> Since the demuxer provides no other means of knowing sync between audio and
> video I suppose it could make sence to use a timebase wich would give this
> completly correct, if video has timebase a/b, then use 1/(1000b) for audio,
> and set dts to frame*1000*a + sync*b. Would that be acceptable?

yes, besides what idiot designed nsv?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In the past you could go to a library and read, borrow or copy any book
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