[Vorbis-dev] Multi-channel labels in Vorbis comments

[Conrad Parker]

On 16 November 2011 18:54, Daniel James <daniel at 64studio.com> wrote:
> Hi devs :-)
>
> At the Mozilla Festival in London recently, I took part in a Hack the DJ
> workshop, looking at ways to take digital DJ'ing to the next level:
> http://www.bbc.co.uk/blogs/researchanddevelopment/2011/11/setting-a-dj-challenge-at-the.shtml
>
> One of the ideas proposed was stem mixing, using multichannel files in
> DJ applications. A proprietary implementation of this idea is Fireplayer
> (http://itunes.apple.com/gb/app/fireplayer-remixer/id367791455?mt=8) but
> this app is built with the intention that users will buy remixable
> versions of (a very limited number of) well-known songs from an in-app
> store.
>
> We would like to work towards a new open standard for stem mixing,
> something that is compatible with sharing our mixes on the open web -
> legally, of course - but could also be used by record labels that sell
> tracks to DJs.
>
> For example, eight channel Ogg Vorbis files where the first two tracks
> are a stereo mix of the drums, third and fourth stereo bass, fifth and
> sixth stereo vocals, and seventh and eighth tracks everything else. This
> means that you can mute or solo individual stems in the mix, giving you
> the versatility of four-deck or eight-deck mixing but without the
> problems of keeping many decks in sync.
>
> It seems that Ogg Vorbis already has all the features we need in a stem
> format for DJs, but there's the question of how we identify individual
> channels within the file. There are conventions for 5.1 and 7.1 surround
> mixes, of course, but we're not aware of any published convention for
> stems. So it would be useful to have a text label for each channel saved
> in a UTF-8 Vorbis comment which could be displayed in applications. I
> was thinking of something like:
>
> CHANNEL1=Drums L
> CHANNEL2=Drums R
> CHANNEL3=Bass L
> CHANNEL4=Bass R
> CHANNEL5=Vocals L
> CHANNEL6=Vocals R
> CHANNEL7=Synth L
> CHANNEL8=Synth R
>
> The labels could be edited for different languages, while preserving the
> audio content - for example if you had a Soundcloud-type site for DJs in
> Russia, you might would want to label the channels in Russian.
>
> Is there any chance that a standard for labelling channels might make it
> into the official Vorbis comment spec? Or would it be rejected as
> 'structured data'?

Hi Daniel,

Sounds like a fun application :)

Rather than a single multi-channel Vorbis file, you could also use a
file with multiple Ogg tracks, each containing a stereo Vorbis stream.
Then you would only need to label each stream once without numbering
or re-assigning stereo channels:

PART="Bass"
PART_RU="бас"

and existing panning, stereo compression etc. would continue to work
for each stream (or indeed, each stream could be surround if that's
your thing). Also it'd be straightforward to losslessly rip out any of
these streams into an independent file, and to merge streams without
re-encoding.

cheers,

Conrad.