[ortc] RTX and ssrc indication

ibc has just created a new issue for https://github.com/openpeer/ortc:

== RTX and ssrc indication ==
According to the spec:

> 9.12.1 Dictionary RTCRtpRtxParameters Members
>
payloadType of type payloadtype
>
The payload type to use for retransmission. If unset, 
RTCRtpCodecParameters.payloadType for the "rtx" codec is used by 
default.
>
ssrc of type unsigned long
>
The SSRC to use for retransmission, as specified in [RFC4588]. If 
unset when passed to RTCRtpSender.send(), the browser will choose.

When it comes to SDP, how is such a SSRC indicated? For example (some 
stuff removed):

```
m=video 62125 UDP/TLS/RTP/SAVPF 100 101 116 117 96
a=sendonly
a=rtpmap:100 VP8/90000
a=rtcp-fb:100 ccm fir
a=rtcp-fb:100 nack
a=rtcp-fb:100 nack pli
a=rtcp-fb:100 goog-remb
a=rtpmap:101 VP9/90000
a=rtcp-fb:101 ccm fir
a=rtcp-fb:101 nack
a=rtcp-fb:101 nack pli
a=rtcp-fb:101 goog-remb
a=rtpmap:116 red/90000
a=rtpmap:117 ulpfec/90000
a=rtpmap:96 rtx/90000
a=fmtp:96 apt=100
a=ssrc-group:FID 2370134951 1456621734
a=ssrc:2370134951 cname:KZloQhO7d7spe7DA
a=ssrc:2370134951 msid:f2ZAO9Z0CX2iYNdVD4EMZ7vr5gGxUQugpRkz 
37d3d6c3-7646-48aa-bdc1-59fa55118a14
a=ssrc:2370134951 mslabel:f2ZAO9Z0CX2iYNdVD4EMZ7vr5gGxUQugpRkz
a=ssrc:2370134951 label:37d3d6c3-7646-48aa-bdc1-59fa55118a14
a=ssrc:1456621734 cname:KZloQhO7d7spe7DA
a=ssrc:1456621734 msid:f2ZAO9Z0CX2iYNdVD4EMZ7vr5gGxUQugpRkz 
37d3d6c3-7646-48aa-bdc1-59fa55118a14
a=ssrc:1456621734 mslabel:f2ZAO9Z0CX2iYNdVD4EMZ7vr5gGxUQugpRkz
a=ssrc:1456621734 label:37d3d6c3-7646-48aa-bdc1-59fa55118a14
```

It indicates that the `RtpSender` can send RTX packets with payload 
`96` for codec VP8 (payload `100`). Since `ssrc-group` is used, should
 I understand that RTX packets for VP8 will be sent with ssrc 
`1456621734`?


Please view or discuss this issue at 
https://github.com/openpeer/ortc/issues/386 using your GitHub account

Received on Monday, 29 February 2016 10:29:25 UTC