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RE: Liaison response - template on MIME type parameter for TimedText

From: Michael Dolan <mdolan@newtbt.com>
Date: Wed, 30 Apr 2014 16:40:16 -0700
To: "'Timed Text Working Group'" <public-tt@w3.org>
Message-ID: <025701cf64cd$8c05d720$a4118560$@newtbt.com>
Nigel, Dave and all-


Is there a TTWG Proposal?


Would “stpp” be registered somewhere where it would be unambiguous from other Codecs strings unrelated to TTML?  I don’t mean the sample entry 4C code, but in the Codecs string namespace.  Wouldn’t it have to be “application/mp4+stpp….”?  Or why not use “application/ttml+xml” (and similar for WebVTT)?


I understand how one could signal profiles of TTML that a document conformed to concurrently, as in the example – all of TTML and EBU-TT.  But the signaling requirements go beyond that – there is often multiple namespaces in use in one document that are not, as an aggregate, a single “profile”. So, these must be explicitly signaled as well since nearly all profiles permit foreign namespaces.  To accommodate this, the “short names” have to be defined as “profiles of namespaces” I think.


For example, if a document uses the CFF-TT text profile of the TTML Full profile, plus SMPTE-TT #608 (US captions), plus CFF-TT metadata, and it was compatible with IMSC, SDP-US and EBU-TT, then it might look like: Codecs=xxxxx.TTMLFULL+IMSC+SDPUS+EBUTT+CFFT+CFFM+SMPTE608.





p.s. I would give the SC29 Secretary a hint about the target of the liaison (MPEG v JPEG).  And, you understand you will not receive a reply until mid-to-late July, right?



From: Nigel Megitt [mailto:nigel.megitt@bbc.co.uk] 
Sent: Wednesday, April 30, 2014 11:48 AM
To: watanabe@itscj.ipsj.or.jp
Cc: Timed Text Working Group
Subject: Liaison response - template on MIME type parameter for TimedText


Dear Mr. Watanabe,


Thank you for your liaison N14444 of April 2014.


We think that we can indeed find a solution together.  We are looking into creating a table of formal "short names" for the profiles of W3C TTML and

the profiles of formats derived from it (such as SMPTE-TT, EBU-TT, and so on).  If MPEG were to propose how to step from the four-character-code of

the sample entry (XMLSubtitleSampleEntry and XMLMetaDataSampleEntry) to something that identifies "a document compatible with one or more profiles of TTML", then we could propose a string composed of a set of one or more these short names as the next parameter.


For example, say W3C defines two profile short names "W3CTTML" and "EBUTTML", and MPEG defines the name "TTML" as referring to the overall

family, one might see




as a codecs string of a file carrying AVC (H.264) and TTML subtitles that

are additionally EBU-TT conformant.


We would check with those deriving from TTML (e.g. at SMPTE, EBU and DECE) if this approach and design are acceptable, before we formalise this.


Kind regards,


Nigel Megitt, David Singer (chairs, Timed Text Working Group, W3C)




Nigel Megitt

Lead Technologist, BBC Technology, Distribution & Archives

Telephone: +44 (0)3030807996 

Internal (Lync): 0807996

BC4 A3 Broadcast Centre, Media Village, 201 Wood Lane, London W12 7TP




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Received on Wednesday, 30 April 2014 23:40:54 UTC

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