Re: OpenAL for flight simulator

Hi Chris,

Chris Robinson wrote:

> It depends on how small of sizes you're talking about. If you have at least 2 
> buffers queued at a given time, that total at least 50ms audio, that should be 
> good enough to get by as long as your code can react fast enough to refill 
> them. However, if you can queue more audio, you would be better off.

Right...assume for the sake of argument that I want to minimize latency, 
e.g. I am streaming so I can apply real-time sw FX based on game play 
(e.g. I have a distortion on an engine sound that gets more, um, 
distorted with RPM, etc.).

(Stop me where I say something truly idiotic...I haven't

If I had a double-buffer callback, my worst latency is 2n where n is the 
number of milliseconds of sound in the buffer.  I hit this case when I 
write the last sample in the buffer...if my write func is infinitely 
fast, I write that last sample n ms before it is played, and I pick up 
just under n ms of additional latency because it's at the end of the buffer.

If I use the minimum number of OpenAL buffers (2) and OpenAL dequeues 
the buffers infinitely fast in its infinitely fast mix function I think 
I pick up 3n ms of latency because once I write a buffer, it sits on 
OpenAL's source Q for n ms before it sits in the non-playing hardware 
buffer for n ms before it is played for n ms.

Do the two buffers include the one being played 'now' or do I actually 
need to keep 2 of 3 buffers filled?

> http://repo.or.cz/w/alure.git/blob/HEAD:/examples/alurestream.c
> It is, of course, subject to change until a proper release is made, but I 
> don't see it changing all that much.

Ah - I see it, and if I understand, this implementation polls at a 
global interval to pick off and refill streams.  The risk there is that 
if I don't poll frequently enough, the wasted time from when I should 
have refilled to when I did refill might be too late and I'll under-run. 
  I suppose in practice the buffers have to be long enough that the 
polling interval would be a non-issue.

cheers
Ben

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