[vorbis-dev] Carrying non-audio data in an Ogg/Vorbis I stream

[Tor-Einar Jarnbjo]

Tirsdag, 29 oktober 2002, skrev du:

>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?

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

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

Tor

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