[Live-devel] payload formats and samplerates in SimpleRTPSink

[Ross Finlayson]

>I've got a question about payload formats in SimpleRTPSink.
>Why is it possible to call createNew with rtpPayloadFormat and 
>rtpTimestampFrequency as arguments?

Because, for dynamic RTP payload format codes (i.e., those >=96), the 
timestamp frequency is not specified, and must be explicitly mentioned.

>Is it ok to e.g. take 0 (pcmu) as rtpPayloadFormat and another samplerate 
>than 8000 although the payloadformat 0 in rfc3550 is defined with 
>samplerate 8000?

No, you shouldn't do this, because payload format 0 is supposed to be for 
8000 Hz mono PCM u-law only.  (If you were to use payload format 0 with 
some other timestamp frequency, or for stereo instead of mono, then 
receivers would have no way of knowing this - because for static payload 
types, there's usually no "a=rtpmap:" line in the SDP description that 
gives receivers this information.)

Instead, if you are streaming PCM u-law with some frequency other than 8000 
Hz, and/or with more than one channel, then you must use a dynamic RTP 
payload code.   For example, see "testWAVAudioStreamer.cpp", line 104.


	Ross Finlayson
	LIVE.COM
	<http://www.live.com/>