[Live-devel] RTP/H264 low latency streaming + source change

[Ross Finlayson]

>I am using Live555 libraries to stream H264 video provided by a 
>frame grabber, via RTP (not RTSP).
>I use VLC and VLC activeX as a RTP/H264 client.
>
>Sometimes, I need to change the camera used by the framegrabber, so 
>I close the RTP sink, the framer, the source, and I open them again 
>with the new video. Doing that, (even with the same video 
>parameters), the client often hang (but not every time), and 
>sometimes go on playing again but with a big delay.
>How can I prevent the client from freezing the video or display the 
>video with delay ? Sending some missing frames ? Special trick to 
>warn client ?
>My main objective is LOW latency, some image skips are not a problem.

I suspect that your problem is caused by the fact that each sending 
camera (server) necessarily uses a different RTP timestamp base, and 
so when you switch to receiving from a new camera, the received 
data's presentation time will briefly be inaccurate, until you 
receive a new RTCP "SR" packet from the new source.  (I'm assuming 
that your servers send RTCP as well as RTP; because you're using our 
software, that should be the case.)

One way to reduce this problem is to increase the average RTCP 
sending frequency, which you can do by increasing the "totSessionBW" 
parameter that you pass to "RTCPInstance::createNew()".  (This 
parameter is intended to represent the stream's bitrate in kbps.  It 
is used - by the RTCP code - to figure out how often to send RTCP 
packets.)
-- 

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/