Audio video sync problem in the multicast mode

[Nathan]

I noticed an interesting problem about the a/v sync or lip sync issue
happened in gstreamer.
We are building hdtv over ip application, and gstreamer will send
audio/video together from transmitter side to multiple receivers 

when there is one receiver, we set the udpsink/udpsrc in the unicasting mode
(see below), the lip sync is perfect.
when there is multiple receivers,  we set the udpsink/dupsrc in the
multicasting mode, the delay between audio and video become uncertain. In
the begining, there is no delay, and after half an hour we lost the lip
sync. 

Why the lip sync behavior like this?
RTCP protocol is used in gstreamer to guarantee audio video sync, and when
there is only one receiver, this receiver(udpsrc) will report rtcp packages,
which contains the timing information to the transmitter（udpsink), then the
transmitter can adjust the delay between audio and video pipeline.
However, when there is multiple receivers, (I might be wrong here) so there
are multiple receivers reporting the rtcp packages to the transmitter. I was
thinking this might be the reason when there is multiple receivers, the lip
sync is gone.

My question is, shoud I set the rtcp related pipeline works in the
multcasting? How the transmitter pipeline handles different rtcp packets
from different receiver?
Please help me out here. I have been stuck with this problem for a while.


Transmitter side:
rtcpsrc, and rtcpsink here are in fact udpsrc and udpsink
/****************************************************************************************************/
	g_object_set(G_OBJECT(app->video_udpsink),  "host",mulcast_address, "port",
VIDEO_udpsink_PORT, "sync",FALSE,"async",FALSE
,"auto-multicast",FALSE,NULL); // video rtp
	g_object_set(G_OBJECT(app->audio_udpsink),  "host",mulcast_address, "port",
AUDIO_udpsink_PORT, "sync",FALSE,"async",FALSE
,"auto-multicast",FALSE,NULL); //audio rtp sink
	
	g_object_set(G_OBJECT(app->video_rtcpsink), "host",mulcast_address, "port",
VIDEO_RTCPSINK_PORT,"sync",FALSE,"async",FALSE
,"auto-multicast",FALSE,NULL); // video rtcp sink
	g_object_set(G_OBJECT(app->audio_rtcpsink), "host",mulcast_address, "port",
AUDIO_RTCPSINK_PORT,"sync",FALSE,"async",FALSE
,"auto-multicast",FALSE,NULL);// video rtcp sink
	
	
	g_object_set(G_OBJECT(app->video_rtcpsrc), "multicast-group",
mulcast_address, "port", VIDEO_RTCPSRC_PORT, NULL);//  video rtcp sink
	g_object_set(G_OBJECT(app->audio_rtcpsrc), "multicast-group",
mulcast_address, "port", AUDIO_RTCPSRC_PORT, NULL);//  video rtcp sink

/****************************************************************************************************/
	app->loop= g_main_loop_new(NULL, FALSE);
    bus = gst_pipeline_get_bus (GST_PIPELINE (app->pipeline));
    gst_bus_add_watch (bus, bus_call, app->loop);
    gst_object_unref(bus);
    

	gst_bin_add_many(GST_BIN(app->pipeline),
app->v4l2src,app->omxbufferalloc,app->omx_h264enc,app->gstperf, app->queue1,
/*app->h264parse,*/app->rtph264pay,app->video_udpsink,NULL);
	gst_bin_add_many(GST_BIN(app->pipeline), app->alsasrc,app->audioconvert,
app->ffenc_ac3,app->queue2, app->rtpac3pay, app->audio_udpsink,NULL);
	
	gst_bin_add_many(GST_BIN(app->pipeline),
app->video_rtcpsrc,app->video_rtcpsink,NULL);
	gst_bin_add_many(GST_BIN(app->pipeline),
app->audio_rtcpsrc,app->audio_rtcpsink,NULL);
//=====================================================================================================


Receiver side:
rtcpsrc, and rtcpsink here are in fact udpsrc and udpsink
        g_object_set(G_OBJECT(app->video_udpsrc),  "port",
VIDEO_RTP_SRC_PORT, "caps", video_caps, "multicast-group", mulcast_address,
"auto-multicast", TRUE, NULL); // video rtp src
		g_object_set(G_OBJECT(app->audio_udpsrc),  "port", AUDIO_RTP_SRC_PORT,
"caps", audio_caps, "multicast-group", mulcast_address, "auto-multicast",
TRUE, NULL); //  audio rtp src
        g_object_set(G_OBJECT(app->video_rtcpsrc), "port",
VIDEO_RTCP_SRC_PORT, "multicast-group", mulcast_address, "auto-multicast",
TRUE, NULL); // video rtcp src
  		g_object_set(G_OBJECT(app->audio_rtcpsrc), "port", AUDIO_RTCP_SRC_PORT,
"multicast-group", mulcast_address, "auto-multicast", TRUE, NULL); //  audio
rtcp src
        
        g_object_set(G_OBJECT(app->video_rtcpsink),"host", mulcast_address,
"port", VIDEO_RTCP_SINK_PORT, "auto-multicast", TRUE,"sync", FALSE, "async",
FALSE, NULL); 
		g_object_set(G_OBJECT(app->audio_rtcpsink),"host", mulcast_address,
"port", AUDIO_RTCP_SINK_PORT, "auto-multicast", TRUE, "sync", FALSE,
"async", FALSE, NULL); 
		







--
View this message in context: http://gstreamer-devel.966125.n4.nabble.com/Audio-video-sync-problem-in-the-multicast-mode-tp4656996.html
Sent from the GStreamer-devel mailing list archive at Nabble.com.