Chunk data definitions are incomplete (VP9, AV1)

[sandersdan]

For VP9, the definition does not allow for superframes (VP9 Annex B) but should. The VP9 spec calls a frame or superframe a "chunk", but this appears to be informal.

For AV1, the OBUs should form a "Temporal Unit", similar to the description in the ISOBMFF binding (possibly we want other requirements from there as well).

In addition, the Opus definition is using "have to" where the other registrations use "expected".