Currently the [`EncodedChunkMetadata` dictionary](https://w3c.github.io/webcodecs/#encoded-video-chunk-metadata) includes `SvcOutputMetadata`, which only supports temporal scalability ([temporalLayerId](https://w3c.github.io/webcodecs/#dom-svcoutputmetadata-temporallayerid)). However, within the Encoded-Transform API, [RTCEncodedFrameMetadata](https://www.w3.org/TR/webrtc-encoded-transform/#RTCEncodedVideoFrameMetadata) includes its own (incompatible) SVC metadata. Here is a comparison of the two approaches: https://docs.google.com/presentation/d/1lFAUSvApbBYfBNJH_xcRW0YjD0aF5T1ZqjyyDJMesJw/edit#slide=id.g1a4ac56601a_3_0 Can we define the complete set of SVC metadata in WebCodecs and then have it inherited by Encoded Transform? Related: https://github.com/w3c/webrtc-encoded-transform/issues/170