[Bug 703560] New: [PATCH] rtpbin: new event for informing downstream about synchronization

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=703560
  GStreamer | gst-plugins-good | 1.1.1

           Summary: [PATCH] rtpbin: new event for informing downstream
                    about synchronization
    Classification: Platform
           Product: GStreamer
           Version: 1.1.1
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: Normal
         Component: gst-plugins-good
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: dv at pseudoterminal.org
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Created an attachment (id=248333)
 View: https://bugzilla.gnome.org/attachment.cgi?id=248333
 Review: https://bugzilla.gnome.org/review?bug=703560&attachment=248333

patch which adds the custom downstream sync event

Currently, rtpbin sends out RTP packets on a best-effort basis until it
receives an RTCP SR packet. Once that happens, the bin is able to synchronize
the packet timestamps. For downstream elements and applications, it is
sometimes desirable to know when the SR packet was received (and therefore when
rtpbin started to output with synchronization).

To accomplish this, this patch adds an option to rtpbin that enables a new
custom in-band downstream event, called "GstRTCPSRReceived". This event is sent
when the rtpbin receives an RTCP packet. (In-band, because out-of-band could
result in the event arriving downstream before the synchronized buffers do.)

One example use case is when an application wishes to drop buffers until the
rtpbin is synchronized. With this patch, the application can hook a probe to an
RTP depayloader's src pad, and drop buffers until it sees the GstRTCPSRReceived
event. Once this is done, the buffer switches from dropping to passing all
buffers.

This is also useful to avoid synchronization problems with an audiosink's
internal counters and timestamps.

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