Vorbis dev - Aug 2001 - Device Control

Hello Folks,

I remember reading sometime ago here about placing alongside the audio stream
other information, such as DMX lighting controls (ave a wee look-see here
http://llg.cubic.org/dmx4linux/ ).  I now have some gear i can get my hands on
to play with and was wondering if anyone else is/has been working on anything
similar.  The emphasis here is on public exhibition displays, where one could
setup lighting on the intended target display as the dialogue plays out from
perhaps an embedded device.

Any pointers would be great!
Cheers,
Kerry.

1,0... my two bits.

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On Wednesday, August 15, 2001, at 11:04 , Kerry Milestone wrote:
> I remember reading sometime ago here about placing alongside the audio 
> stream other information, such as DMX lighting controls (ave a wee 
> look-see here http://llg.cubic.org/dmx4linux/ ).  I now have some gear 
> i can get my hands on to play with and was wondering if anyone else 
> is/has been working on anything similar.  The emphasis here is on 
> public exhibition displays, where one could setup lighting on the 
> intended target display as the dialogue plays out from perhaps an 
> embedded device.
The plan (such as it is) remains the same. Work out a nice packetized 
format for your track data, use libogg to pack it into ogg pages, and 
interleave them with the vorbis stream. As long as the logical bitstream 
id is different, that should fit the spec as intended. I'd suggest 
filling the granulepos with timecodes at the same sample rate as the 
vorbis audio you're syncing with unless your data stream has an internal 
or significantly different sequence number that makes more sense. 
Whatever, as long as the player knows how to sync.

We're still without any infrastructure to support this, so some coding 
is needed. Jack apparently has a contract to integrate midi data, so 
some of it may happen soon. There's also an issue with libvorbisfile 
(and most other player code) in that they currently don't deal properly 
with non-degenerate ogg files, but that won't be an issue for the 
(custom) installation application you mentioned. Likewise, we've not 
solved the 'table of contents' issue, but that only concerns player 
interoperability. I expect if you put the vorbis header first, you won't 
have any problems, and other players can just ignore the dmx track.

Hope that helps,
  -r

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BTW, we've had several questions about DMX light control tracks. Can
anyone comment how useful the midi support will be for this? I know
it's possible to control some lights with midi directly, and that the
formats share some similarities, but I haven't found an actual description
of the DMX protocol or file format, so it's hard to compare.

 -r

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