Re: RTCRtpRtxParameters lacks "apt"

Please, let me refactor my text as it was wrong. Instead of audio and
video with same SSRC (which is 100% wrong) let me talk about a single
stream (let's say video) with two codecs:



So the peer may announce this:

- video h264
  - ssrc = 111111
  - codecPayloadType = 111
  - rtx.ssrc = 111112

- video vp8
  - ssrc = 111111
  - codecPayloadType = 222
  - rtx.ssrc = 111112

Now we receive a RTP packet with SSRC=111112. We don't know whether it
is a rtx for h264 or vp8. And we MUST NOT check its payload-type since
it is supposed to mean:

       <number>: indicates the dynamic payload type number assigned
        to the retransmission payload format in an rtpmap attribute.

This is, the payload in the rtx packet will never be 111 or 222.


So finally the info we need to accomplish this RTX stuff would be
something like:

- video h264
  - ssrc = 111111
  - codecPayloadType = 111
  - rtx.ssrc = 111112
  - rtx.codecPayloadType = 991

- video vp8
  - ssrc = 111111
  - codecPayloadType = 222
  - rtx.ssrc = 111112
  - rtx.codecPayloadType = 992


Now if a RTP packet with SSRC=111112 and payload-type=992 we know that
it is a retransmission of a vp8 packet.


At the end, we need to extend the RTCRtpRtxParameters dictionary:

------------------------
dictionary RTCRtpRtxParameters {
    unsigned long    ssrc;
    payloadtype       codecPayloadType;
};
------------------------



-- 
Iñaki Baz Castillo
<ibc@aliax.net>

Received on Wednesday, 15 October 2014 11:48:44 UTC