[gst-devel] Streaming Lip Sync

Dave Baker dave at accidentalegg.co.uk
Tue Aug 9 16:13:39 CEST 2005


I've just had another play around with flumotion trying to get audio  and 
video in sync on my live stream. I've been trying to do this for months now 
and with no success - I'm now using a BTTV card with the v4l1 interface. All 
the info about how I'm using it is in the config file: 

The latest results are that I've noticed the timestamps of the audio and video 
that MPlayer displays on the console while it's playing drift out whilst 
MPlayer is running. This suggests to me that GStreamer thinks the streams are 
in sync, wheras MPayer is doing the counting and finding that it's getting 
way more audio than video, and trying to sort out the mess. That's my 
analysis, but here are the raw result so you can mull over them yourself (the 
time is just me and a stopwatch started approximately when flumotion was 
started, give or take a few seconds):

Time		Audio	Video
20		15		15
50		41		41
1:20		69		69
3:00		164		144
3:40		192		152
3:52		206		156
4:15		234		164
4:44		262		171
	--MPlayer restarted--
5:10		288		279
5:22		290		281
3:32		304		285
6:24		360		300
7:05		402		312
7:36		430		320
	--MPlayer restarted--
8:05		458		458
8:19		471		461
~15:00	Mplayer gives up and starts ignoring the audio! Message: "Too many 
video packets in the buffer: (4096 in 3939504 bytes)."

I've checked to make sure the formats are ending up the same at both ends - 
video 350x256 25fps, audio 44100Hz, stereo, so it doesn't seem to be video 
played too slowly or similar.

The other interesting thing to note is that the timestamps stay in sync for 
quite a while after flumotion is started, but then move apart much faster 
when MPlayer is restarted. I can't think why this might be - perhaps somenody 
else can.

It's a real shame I haven't managed to get this working as we'd be, as far as 
I know, the first TV station broadcasting worldwide in Theora, which would be 
great for YSTV, GStreamer and Xiph. However this is driving me spare, and we 
need to have this running soon, so this is really my last appeal for help.


Dave Baker

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