[Live-devel] numChannels Parameter

[Ross Finlayson]

>I have a SimpleRTPSink that is fed a transport stream from 
>MPEG2TransportStreamFramer.  That transport stream contains one 
>MPEG-4 video elementary stream plus one MPEG-1, Layer 3 stereo 
>(2-channel) audio stream.  When I call  SimpleRTPSink::createNew(), 
>what value should I use for the numChannels parameter?

When streamed over RTP, a MPEG Transport Stream - regardless of its 
actual contents - is described in SDP as being a "video" stream, and 
therefore the "numChannels" parameter is ignored, but should be set 
to 1.

See, for example, the code in "MPEG2TransportFileServerMediaSubsession.cpp":

return SimpleRTPSink::createNew(envir(), rtpGroupsock, 33, 90000, 
"video", "MP2T", 1, True, False /*no 'M' bit*/);

Note also that - for network efficiency - you should pack as much 
Transport Stream data as possible (but with a granularity of 188 
bytes) into each RTP packet.  Using the default MTU, this usually 
means 7*188 bytes of Transport Stream data per RTP packet.

See, for example, code in 
"MPEG2TransportFileServerMediaSubsession.cpp" (for streaming via 
unicast), or "testMPEG2TransportStreamer" (for streaming via 
multicast).
-- 

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