W3C home > Mailing lists > Public > public-tt@w3.org > May 2014

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

From: David Singer <singer@apple.com>
Date: Wed, 14 May 2014 19:17:08 +0200
Cc: Cyril Concolato <cyril.concolato@telecom-paristech.fr>, TTWG <public-tt@w3.org>
Message-id: <737CF71A-1DC2-41E7-B791-D06B1F3E168E@apple.com>
To: Glenn Adams <glenn@skynav.com>

On May 14, 2014, at 19:14 , Glenn Adams <glenn@skynav.com> wrote:
> > namespaces, yes. But surely SMPTE-TT  and its use of images implies a different processing capability, for example?
> >
> > correct, but that use of namespaces is orthogonal to declaring which profile should be required; if an author requires support for, say, the SMPTE 2052-1:2010 profile, they would need to specify
> >
> > codecs=“stpp.ttml.st10"
> 
> s/requires support for/permits processing by a client that supports/
> 
> but yes, generally
> 
> >
> > assuming that the following registration has been entered into an stpp.ttml registry:
> >
> > "st10" : "http://www.smpte-ra.org/schemas/2052-1/2010/profiles/smpte-tt-full"
> >
> > if the author is willing to accept support for TTML1 DFXP Presentation profile as a backup, then they would need to express it in an appropriate syntax, but I'm not sure from reading RFC6381 how to express this (the semantics of multiple comma separated values for the codecs parameter don't seem particularly well documented);
> 
> Yes, they mean that there are several tracks in the file (video, audio, captions).  You only get one track, so you don’t get to use comma as a separator.  Use something else, like + that I suggested (meaning either/or).
> 
> codecs=“avc1,mp4a,stpp.ttml” means a file with three tracks, one containing AVC (H.264), one containing some sort of MPEG-4 audio, and one containing timed XML sub-titles in the TTML format.
> 
> >
> > if the comma operator means OR (rather than AND), then one might specify
> >
> > codecs="stpp.ttml.st10,stpp.ttml.tt1p”
> 
> That’s two distinct timed-text tracks;  try
> 
> codecs=“stpp.ttml.st10+tt1p”
> 
> or something similar, expressing one TTML track for which either an st10 processor or a tt1p processor are acceptable.
> 
> ok; but does anyone but me wonder if '+' is the best operator? in my mind it is more associated with AND than OR; could we use '|' instead?
>  

I wondered the same thing…

I need to look at what reserved characters there are in MIME parameters.  It would suck to pick something that required escaping in most uses.


David Singer
Manager, Software Standards, Apple Inc.
Received on Wednesday, 14 May 2014 17:17:39 UTC

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