[gst-devel] RTSP stream and seeking operations

[Edward Hervey]

On Mon, 2009-03-16 at 00:09 -0700, Aleksey Yulin wrote:
> Further investigations show that there's the same SEEK issue while trying to
> stream mpeg TS over using the HTTP streaming.
> 
> So it seems that the problem is actually in the Mpeg Transport Stream
> demuxer (we use 'mpegtsdemux').

  That would be "Bug 550634 – [mpeg ts demuxer] Doesn't support seeking
and duration reporting":
  http://bugzilla.gnome.org/show_bug.cgi?id=550634

> 
> As we could see the demuxer creates an initial NEWSEGMENT starting from the
> first TS timestamp for the downstream elements. That works fine, but when
> SEEK is performed the new NEWSEGMENT event is generated before the demuxer -
> in the RTP depayload element. This segment has a 0 as start and actual seek
> position as a 'position'. 

  Wait, you're using a http source or a rtp source ? Why do you need a
rtp depayloader ?

> But the demuxer instead of patching this NEWSEGMENT event (shifting to the
> next known TS packet timestamp) seems to just pass it downstream. This would
> be OK, but the demuxer continues to set buffers timestamps to the actual TS
> packets timestamp so for downstream elements it looks like
> out-of-valid-range buffers are coming so they whether start to skip these
> buffers (like mpeg2decoder) or just returns UNEXPECTED (as mpegaudio
> decoder) causing the pipeline to pause forever.
> 
> We've tried to send the valid NEWSEGMENT event after SEEK (from the
> streaming thread context) and got the following: after seek the picture has
> paused, but after some time (comparable to the new position value) the
> playback started from the new position. This happens only with the first
> SEEK - any subsequential seeks causes the pipeline to pause forever as
> before.


  Doing proper seeking in push-mode (you can do 'immediate'
random-access with an http source) is going to be a lot trickier than
implementing it for pull-mode (from a local file) though.

  If you're interested in getting this feature fixed, I'd recommend
carrying on the discussions in the bug report.

   Edward