[NUT-devel] codec_specific_data

[Rich Felker]

On Mon, Jul 17, 2006 at 11:43:30PM +0200, Michael Niedermayer wrote:
> Hi
> 
> each stream has one global header in nut, matroska and avi 
> too have exactly one global header APIs like the ones from mplayer 
> and ffmpeg and directshow AFAIK are also designed based on a single 
> global header

call the above text (*)...

> but a very small number of codecs are designed so that they have
> several global headers but no standarized way (that i know of) of
> converting them to a single header, the "ogg codecs" fall in this
> category
> 
> several solutions exist:
> 1. store several headers at nut level
> 2. leave it unspecified
> 3. specify how these multi packet codecs should be stored be it in nut.txt
>    or in a seperate file
> 
> if we do specify how these codecs should be stored then we can either
> A. invent our own system (this is for all practical proposes is identical
>    to storing them at nut level)
> B. borrow the system from another container format
> 
> 
> leaving it unspecified will lead to a mess of different systems used by
> different muxers

agree, this is not an option.

> storing them at nut level will need them to be converted to a single
> packet format during demuxing and to a multi packet format during nut
> muxing in most cases

due to (*), all this does it create a huge deal of complexity at the
muxer level for the sake of a few broken codecs. better to identify
them as broken and provide supplemental specs for how to pack the
extradata. this is what was discussed before, anyway.

i've said it many times before, my fundamental law of hacks and
workarounds is that whenever you're integrating a broken component (in
this case the strange codecs) into an otherwise clean system, you
always isolate the hacks to support the broken component as close as
possible to the broken component.

> borrowing another system and using that throughout an application will
> lead to the least converting around

and it will also encourage the adoption of standards that will
facilitate storing these broken codecs in any container, as opposed to
just solving the problem for nut alone. haali seems willing to work
with us on this, and having his support would be great for getting nut
into widespread use.

rich