Re: [payload] new draft - RTP Payload for TTML Timed Text

[Nigel Megitt <[e-mail]>]

Dear IETF Payload group,

This draft was discussed by the W3C Timed Text Working Group (TTWG) on 2019-02-07 [1].

[1] Minutes of W3C TTWG meeting 2019-02-07: https://www.w3.org/2019/02/07-tt-minutes.html#item03

During the meeting concern was raised about the approach to the IANA registered media type, specifically the meaning of section 8. IANA Considerations.

There was consensus amongst the group that the text specifying that this text:

“The media types registry SHOULD be updated to make reference to this document for the application/ttml+xml media type.”

is incorrect and needs to be changed. The media type registration for TTML is owned by W3C and should not be changed by IETF – we note that the change control is clearly marked as being owned by W3C so in that sense this text is inconsistent.

The IANA media type registration itself defers to the TTWG document “TTML Media Type Definition and Profile Registry” [2] which is already referenced by the RTP Payload draft. An improvement would therefore be to update the text in section 8 to suggest that [2] can be updated to include the profiles defined within the payload document. Indeed doing so would result in the creation of a short code for the profile processor mentioned in section 4.2.1.2.1.3 Processor profile signalling.

[2] TTML Media Type Definition and Profile Registry https://www.w3.org/TR/ttml-profile-registry/


The TTWG also discussed two additional concerns without closing on a position at this time:

  1.  A query whether the media type registration information really needs to be copied in at all here or if it can be referenced;
  2.  A request to make sure that the language about profile signalling does not imply that the codecs parameter can denote all profiles, especially in the case that the payload document contains an embedded profile.

TTWG may provide further input on those two points but would welcome further input especially on the first.

Kind regards,

Nigel Megitt as Chair of W3C TTWG




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