[NUT-devel] header packing for xiph codecs

[Michael Niedermayer]

Hi

On Mon, May 07, 2007 at 03:22:17PM -0700, Ralph Giles wrote:
> At some point we talked about there being a general need to pack the 
> necessary decoder initialization headers for codecs like Vorbis and 
> Theora into a single binary blob, and how it would be nice if there were 
> some standard way to do that.
> 
> I've been pushing for something like that in the RTP payload specs, 
> which are going through a new round. So, what do you think of the 
> following:
> 
> - 24 bit "unique id" marking the header for reference
> - number of headers, encoded as a variable-length unsigned integer, 
>   using the 'v' method from the nut spec
> 
> - for each header:
>   * length of the header in bytes, encoded using the 'v' method
>   * header data, padded out to the nearest byte boundary
> 
> Comments please,

well any standardized packing is a big improvement for everyone who has to
deal with xiph codecs in situations where multiple global packets are
not possible ...

your specific suggestion above seems like a fairly simple and flexible
choice

one thing though which id like to say (again) is that the global headers
generally contain only data essential for decoding the stream. and because
of that things like RTP and containers might try very hard to keep them
intact possibly at the expense of startup delay and file size ...
so putting comments, description and other metadata in them is IMO a very
bad idea ...

PS: as a quite off topic note, IMO RTP should be more generic and not
require a new RFC for every codec (this is shitty design IMHO)
if it where just for things like the header packing that would be 
understandable, but looking at for example the 200kb of text needed
to describe h.264-rtp i feel the urge to vomit, 200kb should be enough
to describe a RTP like protocol which supports all current and future
mpeg and h.26x codecs and propriatery variants

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
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