[vlc-devel] [sout developers] VLC streaming violation of MPEG-TS discontinuity flag

Jean-Paul Saman jpsaman at videolan.org
Fri Sep 25 11:10:52 CEST 2015


On Fri, Sep 25, 2015 at 8:15 AM, Ilkka Ollakka <ileoo at videolan.org> wrote:

> On Mon, Sep 21, 2015 at 06:24:12PM +0300, Ilkka Ollakka wrote:
> > On Mon, Sep 21, 2015 at 10:54:01AM +0200, Francois Cartegnie wrote:
> > > Hi Ilkka,
> Hi again,
> > > Can you confirm your own understanding of, especially towards
> > > the end, because "after a continuity counter discontinuity" is not
> clear.
> > If you refer to TS spec, no, I don't think I have that in hand
> > currently or if I tought of that any more when cooked the patch.
> Thanks for the specs that people pointed. After briefly reading that
> section I think I have following understanding. Not sure if it's
> actually the issue you are asking about, and following is quite a lot
> just flow of thoughts when trying to create mental image of the thing:
> - If we have discontinuity indicator on in non-PCR pid, we can just not
>   care about continuity counter. So we can't know packet drops or others
>   using that counter when discontinuity is signaled.
> - For PCR pid continuity counter should always be running correctly.
> - Every non-PCR pid should have at max 2 packets in row with
>   discontinuity_indicator set on
> - After continuity counter discontinuity next packet should be start of
>   new video sequence/avc access unit/audio frame. This doesn't actually
>   clearly mention that packet with discontinuity signaled should be such
>   packet. Assuming if random_access_indicator is set then the same
>   packet also contains new frame/block/video/* start.
>   When reading that random_access_indicator description, I interpret it
>   in a way that discontinuity signaled packet contains the start of new
>   frame.
>   But it's little puzzling on page 23 second last chapter to talk
>   about after continuity counter discontinuity there should be start of
>   new frame in packet.
>   So based on previous assumptions I made in this mail, I assume that it
>   means when pcr pid gets discontinuity signaled it means that same
>   packet that signals it, contains start of new frame with new
>   timestamps and we reset discontinuity counter checking.
I read the specs basically the same as your understanding above.

> > > Seems also the ts demux discontinuity flag on PCR must be handled
> > > differently :/
> Looks like I need lots of paper and pens with different colors to try to
> get my head around that.
> --
> Ilkka Ollakka
> Catharsis is something I associate with pornography and crossword puzzles.
>                 -- Howard Chaykin
> <https://mailman.videolan.org/listinfo/vlc-devel>
> Kind regards,
Jean-Paul Saman
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