[vlc-devel] Re: lip sych problem
serkanboz80 at yahoo.com
Tue Nov 29 15:38:53 CET 2005
Hi to all,
A have 2 questions,
1-)Why bad presentation times in the ES's results in
audio and video synch. problem in RTP streaming.
2-)If this presentation times are bad why players do
not have any sych problems between different medias.
--- serkan bozkurt <serkanboz80 at yahoo.com> wrote:
> Hi DJ,
> I have a questions :
> You are saying that "player plays broken mpg's but
> does not mean it is streamable".
> Can you please explain about in more detail.
> Best Regards..
> --- Derk-Jan Hartman <hartman at videolan.org> wrote:
> > On 28-nov-2005, at 0:14, Ross Finlayson wrote:
> > >> Should add here - RTP streams are actually 2
> > least) different
> > >> streams
> > >> with different payloads
> > >
> > > This is correct.
> > >
> > >> that are not syncronised well (look at live555
> > >> mailing list). I.e - system will "sync on
> > bitrate", not on
> > >> each
> > >> video packet. It means, that LiveMedia free
> > library do not contain
> > >> mechanisms to make A/V sync/resync.
> > >
> > > But this is all completely false. See
> > <http://www.live555.com/
> > > liveMedia/faq.html#separate-rtp-streams>
> > >
> > > Once again: If your original data source (at the
> > server end) has
> > > (i) proper presentation times (corresponding to
> > the 'wall clock'
> > > time generated by calling "gettimeofday()"), and
> > (ii) it properly
> > > implements RTCP, then RTSP/RTP clients that use
> > the "LIVE555
> > > Streaming Media" software - including VLC -
> > get correct,
> > > time-synchronized presentation times.
> > >
> > > If, however, your server does not implement
> > and/or does not
> > > use properly synchronized presentation times to
> > begin with, then
> > > you're SOL. End of story.
> > >
> > > I spent a lot of time making sure that the
> > RTP/RTCP
> > > implementation works properly - to generate
> > correct, time-
> > > synchronized presentation times at the client
> > I wish people
> > > would stop claiming that this doesn't work.
> > The problem here is that there is tons of material
> > in the wild that
> > does NOT have proper timestamping and
> > synchronisation. The fact that
> > lots of this material works in most players, does
> > not mean it is per
> > definition streamable. The fact is the file is
> > BROKEN. People need to
> > understand this. For MPEG material, like 85% is
> > probably broken.
> > DJ
> > --
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> > http://www.videolan.org/vlc/
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