mediasoup - miss match between PayloadTypes - webrtc

Question

I'm trying to use mediasoup to forward RTP streams with room.createRtpStreamer
my problem is that the payload type (for OPUS) I get from producer.rtpParameters.codecs[i].payloadType is 111,
while the one I get on the actual RTP packets is 100 (seen on Wireshark)
I tried to set preferredPayloadType in my server's config, but it seems to make no difference.
Note:
if I hardcode 100 as the Payload Type for the OPUS stream I can view/hear the stream using FFPlay
I'm using Chrome 55 (latest) and mediasoup 2.0.5 (latest)
any help will be appreciated.

Answer 1

The Producer has the RTP parameters decided by the client (browser), so the PT of OPUS is 111 (the default value generated by Chrome).
But, once in mediasoup server, the Consumers associated to that Producer use the RTP parameters given during the room creation. So, if the codecs given to room = new server.Room(codecs) [1] have a preferredPayloadType field, that will be used within the Consumers (otherwise it will be randomly chosen by the server).
So, when you call room.createRtpStreamer() you provide a Producer, and the generated RtpStreamer [2] has an associated Consumer and PlainRtpTransport. So, you should read the rtpStreamer.consumer.rtpParameters rather than the producer's ones.
[1] https://mediasoup.org/documentation/mediasoup/api/#server-Room
[2] https://mediasoup.org/documentation/mediasoup/api/#RtpStreamer

Answer 2

You should have a look at the SDP of the call setup message and check whether you get 111 or 100 for the OPUS payload.
From there you can decide which part has the bug (Chrome or mediasoup).
In the call setup message (initiating the call) check the payload of the OPUS code.
The called party should respond with the same payload number if it accepts OPUS and then both parties should use the same payload number in the RTP packets.

Answer 3

So I found that the payload I get on producer.rtpParameters.codecs[i].payloadType was the original payload and that room.createRtpStreamer changes the payload type.
Ended up doing the below to resolve the issue
// get the payload (type) from the room.rtpCapabilities.codecs.preferredPayloadType for the specific codec
let payload = this.room.rtpCapabilities.codecs.find((c)=>{
return c.name === producer.rtpParameters.codecs[i].name;
}).preferredPayloadType;