[Bug 797304] New: rtpsession: The RTP timestamp in the RTCP Sender Report may be completely wrong

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=797304

            Bug ID: 797304
           Summary: rtpsession: The RTP timestamp in the RTCP Sender
                    Report may be completely wrong
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-good
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: linus.svensson at axis.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Created attachment 373962
  --> https://bugzilla.gnome.org/attachment.cgi?id=373962&action=edit
Reset the RTPSession object in PAUSED->READY

The RTP timestamp used for RTCP Sender Report is generated from a cached
extended RTP timestamp, which in turn is updated for every pushed RTP buffer.
The timestamp generation does not work with a gst-rtsp-server that uses
GST_RTSP_SUSPEND_MODE_RESET.

If the reset suspend mode is used, the server will configure a media and
prepare it in RTSP DESCRIBE/SETUP, which will trigger rtpsource to cache an
extended RTP timestamp. The pipeline will now be set to GST_STATE_NULL.

In RTSP PLAY, the pipeline will be set to GST_STATE_PLAYING again. A new random
offset will be used for the RTP timestamp, but the previously cached extended
RTP timestamp in all RTPSource objects remains, which leads to a situation
where gst_rtp_buffer_ext_timestamp() sometimes return 0. When this happens, the
RTP timestamp in the RTCP Sender Report is completely broken.

I have implemented rtp_session_reset() that will iterate over all it's
RTPSource's and reset them. The important part is to clear
RTPSource.last_rtptime. Does it make sense to reset the whole RTPSession
object?

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