This looks like a very nice effort! On Fri, Sep 4, 2015 at 1:58 PM, Andrew Kelley <superjo...@gmail.com> wrote:
> On Fri, Sep 4, 2015 at 10:43 AM Ian Esten <i...@ianesten.com> wrote: > >> And an observation: libsoundio has a read and a write callback. If I was >> writing an audio program that produced output based on the input (such as a >> reverb, for example), do I have any guarantee that a write callback will >> only come after a read callback, and that for every write callback there is >> a read callback? >> > > I don't think that every sound driver guarantees this. I see that > PortAudio supports this API but I think they have to do additional > buffering to accomplish it in a cross platform manner. > I wrote a lot of the PortAudio code for OS X. I don't recall exactly (it was a long time ago), but I'm pretty sure the only reason I had to use multiple callbacks and "link" them into one PortAudio callback was to support some very odd case, like input from one device and output to another (even there, I think it was fine unless you did something weird, like SR converting only one of them or something). I recall some discussion about my having to do this that indicated that no one else had needed to do it before. I've worked with a few native APIs and PortAudio, and I don't think any API natively has problems with a single callback for read and write as long as you are using the same device. Different devices and, of course, all bets are off. I could be mistaken -- it's been a while, and I haven't used them all. > If you're writing something that is reading from an input device and > writing to an output device, I think your best bet is to use a ring buffer > to store the input. > Personally, I think the single callback is extremely useful for real-time processing -- no need for the extra latency caused by a ring buffer. With two callbacks you could avoid the latency if both callbacks are on the same thread and you know which is going to be called first.... but I suspect that's not guaranteed either. BTW, on this page you say that PA supports SR conversion: https://github.com/andrewrk/libsoundio/wiki/libsoundio-vs-PortAudio I am pretty sure PA won't do that. It does have pretty good support for whatever SR conversion the native platform supports, but it won't do any conversions itself. bjorn -- Bjorn Roche @shimmeoapp
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