[whatwg] Give guidance about RFC 4281 codecs parameter

Dave Singer singer at apple.com
Tue Apr 10 11:21:10 PDT 2007

At 18:33  +1000 10/04/07, Silvia Pfeiffer wrote:
>Recent discussion at Xiph around http://www.ietf.org/rfc/rfc4281
>suggests the use of the following parameters:
># application/ogg; codecs="theora, vorbis"   for Ogg Theora/Vorbis files
># application/ogg; codecs="theora, speex"   for Ogg Theora/Speex files
># application/ogg; codecs="vorbis"                 for Ogg Vorbis files

sounds good;

>and also use the disposition parameter:
># application/ogg; disposition=moving-image; codecs="theora, vorbis"
># application/ogg; disposition=sound; codecs="speex"

what is the 'disposition' parameter?

>>>We did have the discussion over profiles of these codecs;  I
>understand profiles
>>>are not used, but I am still unclear as to which of the following is true:
>>>a) features are never added to the bitstreams, so any release of the decoder
>>>will decode bitstreams made by any release of the encoder (modulo bugs);
>>>b) the decoder release needed is signalled somehow in the bitstream
>('need at
>>>least the April 2005 release or later to decode this file')
>>>c) neither of the above are true, it's left to the users to stay up
>to date, and if
>>>they don't, then, well, that's their problem.
>In reply to this: Xiph has very carefully created and frozen (1st June
>2004) a definition of the theora codec bitstream format, which should
>be persistent for a while to come. So, while it is possible that there
>may be new features added, it is not currently a consideration. There
>are still multiple rounds of software optimisation possible to theora
>encoders before they will require a change to the bitstream format.
>For the case of a bitstream format change, there is version
>information in the header of a theora bitstream. Major and minor
>version numbers are being used similarly to the way that *nix library
>version numbers work - anything with a minor change is backwards
>compatible, but a major change may not be. So, if a major version
>number change was to occur with theora, a new MIME type would probably
>be required, e.g. video/x-theora2.
>I hope this answers the question?

Yes, at least for Theora.  Thank you!
David Singer
Apple Computer/QuickTime

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