[Live-devel] Questions on streaming live H263 videos

[Cristiano Belloni]

Hi to everybody,

I've got a couple hopefully basic questions about live streaming with 
live555.

I'd like to stream h263-encoded videos to various media players (mainly 
realplayer on mobile phones).

What I do now is starting a thread that captures live frames and encodes 
them in H263 with ffmpeg. The thread writes on a Unix named pipe (FIFO).
Then I create a RTSPServer instance, create a ServerMediaSession and add 
a subsession, passing the FIFO file name as the subsession parameter.

A few problems arise, in order of importance:

1) VLC and Mplayer are able to play the live video, while RealPlayer 
isn't. I captured the network conversation with wireshark, and it seems 
the RTSP negotiation is done correctly, but the server just won't send 
RTP packets (while with VLC or MPlayer it does).

Here's the captured RTSP conversation:

User-Agent: RealMedia Player/mc.28.16.01 (s60; epoc_av21_thumb)
CSeq: 1

RTSP/1.0 200 OK
CSeq: 1
Date: Mon, Dec 17 2007 11:26:51 GMT
Public: OPTIONS, DESCRIBE, SETUP, TEARDOWN, PLAY, PAUSE

DESCRIBE rtsp://217.133.231.30/H263ESVideoTest RTSP/1.0
x-wap-profile: "http://nds1.nds.nokia.com/uaprof/NN70-1r100.xml"
ClientID: RealOnePlayer_s60.28.16.01_21-Apr-2006_10:28:59_epoc_av21_thumb
Accept: application/sdp
Bandwidth: 298368
GUID: 00000000-0000-0000-0000-000000000000
User-Agent: RealMedia Player/mc.28.16.01 (s60; epoc_av21_thumb)
CSeq: 2

RTSP/1.0 200 OK
CSeq: 2
Date: Mon, Dec 17 2007 11:26:51 GMT
Content-Base: rtsp://217.133.231.30/H263ESVideoTest/
Content-Type: application/sdp
Content-Length: 384

v=0
o=- 1197890794075912 1 IN IP4 217.133.231.30
s=Session streamed live by "rtspServer"
i=H263ESVideoTest
t=0 0
a=tool:LIVE555 Streaming Media v2007.12.06
a=type:broadcast
a=control:*
a=range:npt=0-
a=x-qt-text-nam:Session streamed live by "rtspServer"
a=x-qt-text-inf:H263ESVideoTest
m=video 0 RTP/AVP 96
c=IN IP4 0.0.0.0
a=rtpmap:96 H263-1998/90000
a=control:track1
SETUP rtsp://217.133.231.30/H263ESVideoTest/track1 RTSP/1.0
x-wap-profile: "http://nds1.nds.nokia.com/uaprof/NN70-1r100.xml"
Transport: RTP/AVP;unicast;client_port=26022-26023;mode=play
User-Agent: RealMedia Player/mc.28.16.01 (s60; epoc_av21_thumb)
CSeq: 3

RTSP/1.0 200 OK
CSeq: 3
Date: Mon, Dec 17 2007 11:26:52 GMT
Transport: 
RTP/AVP;unicast;destination=217.201.153.216;source=217.133.231.30;client_port=26022-26023;server_port=6970-6971
Session: 1

PLAY rtsp://217.133.231.30/H263ESVideoTest/ RTSP/1.0
Range: npt=0.000-
Session: 1
User-Agent: RealMedia Player/mc.28.16.01 (s60; epoc_av21_thumb)
CSeq: 4

RTSP/1.0 200 OK
CSeq: 4
Date: Mon, Dec 17 2007 11:26:52 GMT
Range: npt=0.000-
Session: 1
RTP-Info: 
url=rtsp://217.133.231.30/H263ESVideoTest/track1;seq=1723;rtptime=1928192185

(The client was RealPlayer from a Nokia N70 mobile, same behaviour with 
RealPlayer for Linux on the same host of the server, so it's not a 
network problem).

The client will then send RTCP control packets regularly, along with 
some strange RTP packets with payload = 73, but the server won't send 
any RTP or RTCP packet, even if the PLAY command was accepted by the server.

2) VLC and Mplayer correctly view the live video, but they often will 
play a chunk of it, then "freeze" the frame for a few seconds, then play 
another chunk, then freeze again. What could the problem be? Buffering? 
Too many packets? (I acquire at 25 fps, but vlc is on the same host as 
the server). Please note all this problems disappear when i stream from 
a file containing raw h263 data @ 25 fps.

3) In my naive implementation, I start the encoder thread after adding 
the subsession and before the taskScheduler().doEventLoop() call. I'd 
like, instead, to start my decoder thread when and only when a client 
does a request for the stream (sparing resources when the server is 
idle), in an "on demand" fashion.

How can I do that? I thought about starting the decoder thread in 
specialClientAccessCheck method, subclassing RTSPServer class, but I 
don't think it's the right way to do it (after all, 
specialClientAccessCheck is for checking IPs and request URLs).



Best regards and thanks in advance for your help,

Cristiano.

-- 
Belloni Cristiano