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

[Tor-Einar Jarnbjo]

Mandag, 28 oktober 2002, skrev du:

>I don't understand how per-packet metadata makes any difference here. 
>The demux happens at the Ogg level, and yes it has too peek at the 
>headers to see which codec to hand each stream to. How is that 
>different?

The JMF is a "pluggable" API, where demultiplexing and decoding is 
completely separated, and the different plugins are unaware of eachother.
A demultiplexer plugin must take an input stream and split it into 
any number of output streams, and it also has to determine the content 
type of each output stream, and if there are more output streams,
which are to be synchronized, each output stream has to know its 
current media time.

With the Ogg file format, this causes at least the following problems:

- Since the demux has to know the content type of each resulting 
output stream, the Ogg demux has to contain logic, to "peek" into 
the logical streams and try to determine the content type, although 
these steps are completely separated in the API, and the demux should 
not really be concerned about the actual content.

- The demux has to know quite a lot about the content format to be 
able to tell the current media time. In Ogg/Vorbis, the time for 
an audio packet is calculated using the granule position in the ogg 
framing, the sample rate and the number of PCM samples in each audio 
packet. Without parsing the Vorbis stream, the demux is not able 
to determine the sample rate and the number of samples in each packet.

<p><p>Tor

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