RTCEncodedVideoFrameMetadata spatialIndex and temporalIndex are not described

[youennf]

It would be good to describe these two properties.
While the encoder can give that information on sender side, this information may be used to generate RTP packets.
And on receiver side, it can be populated from RTP data.

• Using https://www.rfc-editor.org/rfc/rfc9626.html
• VP9: https://www.rfc-editor.org/rfc/rfc9628.html#name-vp9-payload-descriptor
• AV1: https://aomediacodec.github.io/av1-rtp-spec/v1.0.0.html#dependency-descriptor

[youennf]

https://w3c.github.io/webrtc-encoded-transform/#dom-rtcencodedvideoframemetadata-width and https://w3c.github.io/webrtc-encoded-transform/#dom-rtcencodedvideoframemetadata-height are not defined either.

[fippo]

https://w3c.github.io/webrtc-encoded-transform/#dom-rtcencodedvideoframemetadata-width and https://w3c.github.io/webrtc-encoded-transform/#dom-rtcencodedvideoframemetadata-height are not defined either.

see #138, in particular that parsing bitstreams is undesirable. The implementation of what became RFC 9626 has been removed from libwebrtc years ago.