PSA: removing entire m= sections via SDP munging is going away in M138

[Philipp Hancke]

(If you’re not modifying SDP, you can stop reading now)

The standards for WebRTC have always said that the SDP produced by createOffer/createAnswer MUST be passed unchanged to setLocalDescription 

https://datatracker.ietf.org/doc/html/rfc8829#name-modifying-an-offer-or-answe

https://w3c.github.io/webrtc-pc/#dom-peerconnection-setlocaldescription step 4.2

Unfortunately, this has not been policed in Chromium in the past. As of

https://chromiumdash.appspot.com/commit/5edfd244fed9a339f6279cdccb4d57d0c6749b21

which landed in todays M138 canary removing an entire m= line between createOffer/createAnswer and setLocalDescription will result in an error.

If you have any concerns please leave a note on

  https://issues.webrtc.org/issues/416088632

The usage was negligible so we do not expect much turmoil.

[Feng Wang]

I think SDP Munging is very common, and its standardization should be fully discussed with the community. After having a comprehensive and clear plan, we should first make it public, and then make changes, rather than doing it the way it is now, suddenly issuing a PSA saying that the next version is going to be released, which simply doesn't leave enough time for applications to adapt.

[Feng Wang]

I checked the usage of RTCLocalSdpModification and GetUserMedia on Chrome Status, and their usage ratios seem to be equal. From the data, the usage of SDP Munging is very widespread.

By the way, why did the usage of RTCLocalSdpModification increase rapidly after November 2024?