The WebRTC Encoded Transform API allows processing of encoded data from RTCPeerConnections. However, one functionality is lacking: the ability to create new encoded frames from scratch.
So far, the only way to create a new frame has been to read a frame from an RTCPeerConnection. Some use cases require the ability to create frames from scratch. For example, applications that want to do encoding using WebCodecs or some other custom mechanism (e.g., a WASM encoder).
RTC Encoded Frame constructors aim to provide constructors that allow creating RTCEncodedVideoFrame and RTCEncodedAudioFrame objects from scratch, so that applications that want to perform custom encoding of RTC media using WebCodecs or other custom codecs can easily turn the result into RTC encoded frames.