[gstreamer-bugs] [Bug 565319] New: rtpjitterbuffer: bursty reception can cause time to be reversed

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-bad | Ver: 0.10.21
           Summary: rtpjitterbuffer: bursty reception can cause time to be
                    reversed
           Product: GStreamer
           Version: 0.10.21
          Platform: Other
        OS/Version: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: arnout at mind.be
         QAContact: gstreamer-bugs at lists.sourceforge.net
     GNOME version: Unspecified
   GNOME milestone: Unspecified


Please describe the problem:
In rtpjitterbuffer's calculate_skew, buffer timestamps are shifted with a skew
value that changes over time.  However, it is possible that the skew changes
more than the time between buffers, which causes buffer timestamps to go back
in time.  

While running, this is very unlikely to occur due to the large weighting factor
of the running average.  It can occur, for example, when network latency
(temporarily) increases, and the skew grows to e.g. 6s.  Then, suddenly, all
these packets arrive in a burst, which causes delta (the difference between
sending and receiving clock) to shrink suddenly to e.g. 6ms.  The new skew will
then be 6000*124/125 + 6 = 5958ms, and the buffer timestamp is set at 2ms less
than the previous buffer timestamp.

On the other hand, while the window is filling, this can occur very easily. 
Indeed, at that point the weighting factor decreases parabolically, so that the
weighting factor approaches 0 when the window fills up.  Therefore, when rtp
packets come in in a burst while the window is filling, the skew shrinks
quickly.

Steps to reproduce:


Actual results:


Expected results:


Does this happen every time?


Other information:


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