[vorbis-dev] Re: [theora-dev] Re: Ogg Internet Drafts - create application/ogg-vorbis, application/ogg-tarkin, etc.

[Tor-Einar Jarnbjo]

Fredag, 3 januar 2003, skrev du:

>Ogg has always appeared to me to correspond only to the _track media_ 
>and _sample_ layers of a QuickTime movie.  So you still need to know 
>what all the CODECs are and how to use them individually to 
>manipulate what should be general data in the file.  Please, somebody 
>correct me if I'm wrong.

I have asked the same questions here on the mailing list assuming 
the same as you do, and yet noone has been able to explain that it 
is not so.

In the media frameworks I've been working with, the demultiplexer 
must not only be capable of splitting a physical stream into logical 
streams, but also be able to tell the mime type of the logical stream 
and ideally also put an absolute, comparable time stamp on the logical 
stream packets.

In the case of Ogg, this means that the demultiplexer must peek into 
the logical stream and based on the binary data try to determine 
what sort of content it contains. It is not possible to simply add 
a new decoder to support a new format. The only other possible solution 
I come to think of would be (and it's not a very practicable solution) 
if the framework loads every available decoder to check if it is 
able to decode this stream. It might not even be possible if the 
stream is not seekable.

To put a time stamp on a Vorbis audio packet, the demultiplexer has 
to parse and understand the Vorbis header and every audio packet 
to get the stream's sample rate and the audio packet length in order 
to calculate a real time stamp based on the granular position. 

<p>Tor

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