The WebCodecs Codec Registry defines the contents of an EncodedAudioChunk and EncodedVideoChunk for the audio and video codec formats in the registry. The "internal data" in these chunks is used directly in this specification as the "LOC Payload" bitstream. This "internal data" is the elementary bitstream format of each codec without any encapsulation.
This is one section of Low Overhead Media Container, rendered per-section for quick reference and citation. The authoritative text is draft-ietf-moq-loc-04 at the IETF.