Michael Niedermayer <michaelni@gmx.at> writes:
> > On a related subject, it might also be useful to define > > the channel disposition when there is more than one. Mono > > and stereo can go by with the classical default, but as > > soon as there is more channels it is really unclear. And > > imho such info could still be usefull with 1 or 2 > > channels. Something like the position of each channel in > > polar coordinate (2D or 3D?) should be enouth. > > I agree > What about that LFE channel thing?
I was thinking about simply setting the distance to 0, however a flag for "non-directional" channels might be better.
This is wrong, LFE is not about direction but about the type of speaker. LFE stands for "Low-frequency effects". If id move a other random speaker at disatnce 0 and the LFE one out and switch channels it wont sound correct ...
> And where do we put this info, The stream header seems the logic > place if you ask me ...
I agree, this is essential information for proper presentation it definitly belong there.
Good, now we just need to agree on some half sane way to store it. for(i=0; i<num_channels; i++){ x_position s y_position s z_position s channel_flags v }
CHANNEL_FLAG_LFE 1
seems ok?
I'm not convinced this is the right way to go. Consider a recording made with several directional microphones in the same location. Using spherical coordinates could be a solution.
The above was intended to specify the location of the speakers not microphones.
I'm having a hard time imagining a player moving my speakers around depending on the file being played.
And spherical coordinates would just drop the distance, thats the same as setting the distance to 1 and storing that as xyz.
Spherical coordinates without radius needs only two fields.
True, but that gets tricky with integers and precission.
Use rational numbers. That's essentially what you suggest below anyway.
Actually the main reason why i didnt use spherical is that with integers theres a precission to decide on or you end up with rationals. And this somehow starts looking messy ...
I don't see any fundamental difference. If restricted to integer coordinates, an arbitrary point can be described only with a certain precision, regardless of coordinate system.
True but if you map the points to a sphere, then x,y,z gives you arbitrary precisson on the surface of the sphere while with spherical coordinates this needs some additional "tricks". Thus x,y,z give you arbitrary directional precission at quite low complexity.
I didn't realise you were only interested in direction. Not that I know what you'd use the distance for, or how.
Whatever the coordinate system, the location and orientation of the listener must be specified, even if there is only one logical choice.
of course right_position s forward_position s up_position s
And "the listener is at (0,0,0), (1,0,0) is right, (0,1,0) is forward, (0,0,1) is up"
You're forgetting the measurement unit, i.e. metres, feet, etc.
Hmm, I was thinking that only x/y, x/z that is the direction would matter. If theres some sense in also storing distance then we would need a 4th variable to specifiy the precission like: (x/p, y/p, z/p) meter
We can surely do this if someone thinks this is usefull.
I don't think it's useful, but there's no telling what people who measure the copper purity of their speaker cables might believe. -- Måns Rullgård mans@mansr.com