What timestamp does generateKeyFrame return when its promise resolves?

[guidou]

The spec says:

Resolve task.[[promise]] with frame’s timestamp

But a frame's timestamp is not defined in the spec.
RTCEncodedFrameMetadata and RTCEncodedVideoFrameMetadata define several timestamps, the most relevant of which seem to be the rtpTimestamp and timestamp.

An older version of the spec also defined a timestamp field in RTCEncodedVideoFrame, which was removed and replaced by the rtpTimestamp field in RTCEncodedFrameMetadata.

Existing implementations resolve the promise with rtpTimestamp. If this is the intent, we should update the spec to be clear about this.

cc @jan-ivar @youennf

[youennf]

I believe this is indeed the intent, though there is discussion to resolve with undefined instead.

[fippo]

https://www.w3.org/2022/09/13-webrtc-minutes.html#t07 said "don't return a timestamp" which avoids the question which rtp timestamp to return for simulcast.

[jan-ivar]

Overtaken by #275