Clarify normative aspects of TS header and AF fields

[cconcolato]

The DVB draft specification for AV1 mentions that:

• payload_unit_start_indicator shall be set to 1
• adaptation_field_control bits shall be set to "11"
• The random_access_indicator shall be set to 1 when the PES packet contains an AV1 KeyFrame
• The elementary_stream_priority_indicator and intra frame interact

It's unclear why these statements are not in the AV1-MPEG-2 TS specification. Could these be different outside of DVB environments?
In any cases, the specification should talk about these fields: either to mandate the behavior or to indicate that the behavior can vary depending on application environments.

[cconcolato]

Current DVB text is:

and

[tbiat]

payload_ ==> It's implicit and obvious.
adaptation_field_... ==> dvb mandates the adaptation field for random access AV1 DVB_RAP, we might not need it for other TS-based applications.
Decision : share the DVB spec part related to this with the group. Revisit next week.

[tbiat]

We don't want RAP in this spec to conflict with AV1 DVB-RAP.
Put a note : recommended practice / 'should contain'.
Decision : take offline with Cyril. Propose a wording by email for approval.

[cconcolato]

The spec says:

A PES shall encapsulate one, and only one, AV1 access unit as defined in clause 4.3.
We could add a note that says "as a consequence, the PUSI is set to 1"

The spec does neither mention 'adaptation_field_control' nor 'random_access_indicator', not even "random". We should at least have: "When the random access indicator is set to 1, the AV1 access unit shall contain an AV1 Key Frame".