[ogg-dev] Feedback on XML metadata namespace

Ralph Giles giles at xiph.org
Sat Sep 8 11:07:39 PDT 2007

On Sat, Sep 08, 2007 at 07:38:22PM +0200, Daniel Aleksandersen wrote:

> Please explain how oggserials works. If all items (audio, text, images, ...) 
> in an Ogg stream can be described using oggserials; than a oggserial 
> attribute should be used instead of a more generic URI attribute.

That's not a bad idea. Ogg serial numbers must be unique within a 
stream, so this would work.

Brief explaination: You can have any type of time-based media wrapped in 
the Ogg container. This is known as a "logical stream". That can be an 
Ogg stream on its own, but there are also two kinds of mixing you can 
do. First, you can multiplex two or more logical Ogg streams together, 
indicating that the tracks are meant to be played back contemporaneously.
Second, you can concatenate two or more Ogg streams, indicating that the 
individual streams are to be played in succession, like chapters in a 

The serial number field labels each chunk of data as belonging to a 
particular logical Ogg stream. If they're not unique in a multiplexed 
segment nothing works. They're also supposed to be unique among 
concatenated (usually called "chained") segments. Playback generally 
works if they aren't but seeking doesn't.


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