RegisterCodec can register two different codecs with same payload type

[itzmanish]

Your environment.

• Version: feeeebf
• Browser: Chrome/132.0.0.0
• Other Information - https://gophers.slack.com/archives/CAK2124AG/p1737531701059119

What did you do?

I added two different codecs with the same payload type and upon negotiation with the browser the browser threw Failed to parse SessionDescription. a=rtpmap:100 VP8/90000 Duplicate payload type with conflicting codec name or clock rate error.

What did you expect?

RegisterCodec should have returned an error and should not add codec with duplicate payload type.

What happened?

The addCodec method is called from updateFromRemoteDescription and RegisterCodec as well. The issue is if there are different codecs with the same payload type, for eg- 100 VP8 (Firefox) and 100 VP9 (Chrome), getting registered.

webrtc/mediaengine.go

Line 249 in feeeebf

if c.MimeType == codec.MimeType && c.PayloadType == codec.PayloadType {

This line will treat them as different codecs and add both of them in codecs slice.
When the getCodecsByKind method is called during SDP generate for either answer or offer, both codecs will be included in SDP. Chrome throws an error Failed to parse SessionDescription. a=rtpmap:100 VP8/90000 Duplicate payload type with conflicting codec name or clock rate when it gets the same payload type with different codec information.