[ogg-dev] [Vorbis] MT9 Capabilities

Silvia Pfeiffer silviapfeiffer1 at gmail.com
Mon Aug 18 15:46:11 PDT 2008

To add some more information to this thread:

* Ogg allows multiplexing of any number of audio, video, timed text
(subtitle, annotation, karaoke) etc tracks (also called: logical
bitstreams) together in one Ogg physical bitstream

* Skeleton is a header that marks for such a complex Ogg physical
bitstream what logical bitstreams are actually inside the file:

* also, at the last FOMS workshop we defined ROE-
http://wiki.xiph.org/index.php/ROE - a rich way to describe the
relationships between the different logical bitstreams; it would help
a player decide what to play back and how; the only implementation of
ROE is so far in Metavidwiki, e.g. if you click the little caterpillar
image at the top right at
Full ROE spec as it currently stands is here:

As for trying to adjust volumes on the different tracks (as per the
original request) all you really need is an application that can
separately control for a multi-track Ogg audio file the volumes on the
different tracks (the multitrack Ogg file should come with a

If you wanted to store the volume changes back to a file and re-play,
you have several choices. You could extend ROE with a means to
describe the volume changes, or you could define a new annotation
track that would describe the volume changes of the different skeleton
tracks, or you could add the volume changes to the meta headers of a
CMML track (see
http://www.annodex.net/TR/draft-pfeiffer-cmml-03.html), or you could
re-encode the audio tracks at the changed volumes, and there's
probably a number more that I haven't considered yet. What's the best
option? To be honest, I don't know - that depends on your goals and
how you want to implement the application.

BTW: you could try and play around with gstreamer and filters on the
different tracks of a multi-track Ogg file to get track-level volume
changes happening. That would probably already provide what your need
for the playback part of it.


On Mon, Aug 18, 2008 at 10:25 PM, Gregory Maxwell <gmaxwell at gmail.com> wrote:
> On Mon, Aug 18, 2008 at 6:36 AM, Danny Piccirillo
> <danny.piccirillo at ubuntu.com> wrote:
>> Sorry, but i wasn't sure the best place to post this. I was looking for some
>> forums but it doesn't look like Xiph has any official ones. Anyways, i heard
>> about this MT9 think a while ago and i thought it would be awesome if FLAC,
>> Vorbis, and all could implement something like this.
>> http://www.guardian.co.uk/music/2008/may/27/news.seanmichaels
>> http://en.wikipedia.org/wiki/MT9
>> In combination with that, it would also be cool to have some sort of
>> subtitles-esque thing for audio which would be useful for speeches and
>> karaoke.
>> These two things would be a very very big boost for free audio formats :)
>> How feasible is this in the long run?
> Vorbis supports 255 channels in a single stream, FLAC 8. Ogg would let
> you encapsulate many streams in one file, even combining Vorbis, FLAC,
> and Speex.  The open questions are application support and metadata
> for signaling the right default settings.
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