CODEWITHSUNDEEP
webrtcrtx
Leo9988
Leo9988

Reputation: 11

Why does Webrtc RTX need different payload type

upon viewing the webrtc RTX rfc

The payload type is dynamic. If multiple payload types using retransmission are present in the original stream, then for each of these, a dynamic payload type MUST be mapped to the retransmission payload format. See Section 8.1 for the specification of how the mapping between original and retransmission payload types is done with Session Description Protocol (SDP).

but why? if retransmission use a different ssrc, using same payload type as media payload type would not affect the recovering process,right?

Just want to know the design reason behind this approch!

Upvotes: 1

Views: 744

Answers (1)

Philipp Hancke
Philipp Hancke

Reputation: 17275

While you could theoretically use the same payload type and demultiplex by SSRC instead of payload type, SDP can not properly express this as you would end up with two rtpmap lines with the same paylaod type but different codec names.

(one of the downsides of that requirement is that you need one RTX payload type per media type instead of just a single RTX payload type)

Upvotes: 1

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