[Portaudio] adding latency parameter to Pa_OpenStream()

[Phil Burk]

Hello John,

I'm confused by your latest letter.

I wrote:
> > To include your idea within the existing API, we could pass these to
> > Pa_OpenStream as numBuffers:
> > #define PA_LATENCY_WHATEVER   (0) /* or _NO_OPINION or? */
> > #define PA_LATENCY_LOW       (-1)
> > #define PA_LATENCY_HIGH      (-2)

You replied:
> No, I wouldn't suggest doing this, at least not for me -- I have no
> use for it, since I would always compute a numBuffers value based on
> the latency the user supplies, or defaults.

But that is basically your idea except it uses an existing parameter and
integer constants instead of double constants.

You had said:
> drivers are able to handle latency requests, is there any interest
> in adding a latency parmameter to Pa_OpenStream()?
>         This would have the attributes:
> -- A double, with units in seconds
> -- Special constants (coded as negative double values) to indicate:
>    * no opinion about latency
>    * generic "high-latency" for audio streaming
>    * generic "low-latency" for interaction

Aren't we basically saying the same thing? I'm just trying to overload an
existing parameter with the new functionality.

> But, if the user wants
> to push the latency of the system beyond "recommended", I want for
> that attempt (via the -latency command-line option) to have the
> intended effect.

Maybe we need both. Because if the app writer doesn't give a way for the
user to control that minLatency parameter, then they might be stuck with
glitchy audio.

How about:

PaError Pa_SetMinimumLatency( double seconds );

The implementor can also provide an optional back door using an environment
variable like PA_MIN_LATENCY_MSEC if they want.

Phil Burk