Subject: [AVT] Using two or more RTP payload formats

From: Alejandro Cabrera Obed <[email-masked]>
Date: Wed, 15 Dec 2004 17:04:30 -0300

Dear people,

Sorry for my newbie's question but I'm entering the streaming media world.

Just one short question: suppose I want to apply the RTP Payload
format for Uncompressed Video and also I'd want to apply the RTP
Paylod format for FEC to my RTP transport packets....Is it possible to
apply 2 or more RTP payloads format at the same time and to the same
RTP flow/session ???

Because I often saw one RTP payload format applied at a time....

(In the negative case what can I do then to transport uncompressed
video and FEC on a RTP flow ???)

Thanks a lot,

Alejandro Cabrera Obed

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: Magnus Westerlund <[email-masked]>
Date: Thu, 16 Dec 2004 13:01:28 +0100

Hi Alejandro,

RTP is designed to enable the usage of multiple payload types in the 
same RTP session. The usage of multiple payload types, is for example an 
result of desiring to use multiple payload formats or use multiple 
configurations of a payload format. The reason you usually see only a 
single payload format is that most applications is happy with a single 
one per RTP session.

This should be rather obvious from the SDP examples that are present in 
many RTP payload formats, especially the more generic ones. For example 
RFC 2733 has in section 11.2 the following SDP example:

    m=audio 12345 RTP/AVP 121 0 5 100
    a=rtpmap:121 red/8000/1
    a=rtpmap:100 parityfec/8000
    a=fmtp:121 0/5/100

However do please note that for example RFC 2733 provides two different 
choices of multiplexing, either in separate RTP sessions or as in the 
above example using RFC 2198.

Cheers

Magnus

-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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