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laurilo / draft-ilola-avtcore-rtp-v3c

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Issues with SDP grouping #18

Closed laurilo closed 7 months ago

laurilo commented 7 months ago

I don’t know if this document has been sent to, or will be sent to, the SDP directorate, but I believe that there is an issue with the grouping framework usage in Section 9.2:

It seems like the document is defining a new syntax for the SDP group attribute, which is not aligned with RFC 8866.

The document does define a new group attribute semantics value, “V3C”, which is fine, but the attribute must still be aligned with the syntax defined in RFC 5888:

       `group-attribute     = "a=group:" semantics *(SP identification-tag)`

So:

      `a=group:V3C 1 2 3 4`

…would be fine, but:

      `a=group:V3C 1 2 3 4 v3c-parameter-set=AQD/AAAP/zwAAAAAADwIAQ5BwAAOADjgQAADkA==`

…is not. You can’t have parameters after the identification-tags.

The document says that it “extends” the grouping mechanism, but any extension must be done following the extension rules defined for the mechanism. And, RFC 5888 does not define a way for extending the SDP group attribute (apart from defining new semantics values).

laurilo commented 7 months ago

Good catch. the ability to add further parameters in the group attribute was removed from the spec making it better aligned with the group attribute definition from RFC5888.

Further clarification was added in the draft to suggest storing these parametes in the media format parameters of the V3C atlas component media or V3C video component media lines. These were already supported previously, just added more text to explain how the parameters should be handled.

laurilo commented 7 months ago

Resolved with https://github.com/laurilo/draft-ilola-avtcore-rtp-v3c/commit/11780da5bd1f9d23b42bca258d973b0ad123e432