AW: AW: [vorbis-dev] Chained streams and granule position

[Alejandro G. Belluscio]

Hello Tor-Einar,

Tuesday, November 12, 2002, 8:29:23 PM, you wrote:
>> PD: You never answered my last question about the JMF :-)

TEJ> Hmm, must have missed that one. What was it?
TEJ> Tor

[Context of the question]

>>I don't quite understand. If the demux must return the content type,
>>it must know about all data type, or the file format must include an
>>explicit "type" field in the header of each stream. But then it either
>>must know all the mappings from "type" to "codec" or the codec must
>>know all it's magic numbers in different file formats. What am I
>>missing?

TEJ> Exaclty. It would have made sense in Ogg, if each logical stream 
TEJ> would have some sort of header containing information about the content 
TEJ> type. The WAV and AVI formats contain such information.

TEJ> The JMF has a sort of registry, where all demux and codec plugins 
TEJ> are registered. When playing back an Ogg file, the framework knows 
TEJ> from the ending .ogg that the file has a content type of application/x-
TEJ> ogg and searches for a demux plugin supporting this format. An Ogg 
TEJ> demux plugin would examine the file and tell the framework something 
TEJ> like "I've found one logical stream of type audio/x-vorbis". The 
TEJ> framework will then look for a codec plugin supporting that input 
TEJ> format, and if necessary even chain more codecs to produce an output 
TEJ> format, which is supported by the last drain.

I think I understand, I have a last couple of question and I will stop
bugging you ;-). First:
How does the demux knows that type id magic number xxxx corresponds to
application/vorbis? Let's say that you have put your vorbis-pluging,
who registers for application/vorbis. Now, somebody implements vorbis
on wav, and so they put a new number on the wFormatTag field, lets say
x0123. Specifically, who's in charge of determinig that
wFormatTag=x0123 means 'application/vorbis'? The codec (in which case
he should know about all the file types on which he is implemented) or
the demux (in which case he needs to know about all the decoders that
he supports)?

Second question: have you read the thread I posted about?
http://www.xiph.org/archives/theora-dev/200209/0040.html

Reagards,
Alejandro Belluscio

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