Re: sndio play multiple wav files ?

On Fri, Jun 05, 2026 at 04:09:53PM -0400, Paul Wisehart wrote:
> Hi!,
> 
> I am working on a curses C sndio app to
> play samples that are just wav files.
> I would like to be able to play them
> "over each other" like not sequentially.
> 
> (I would like for the wav file to play
> regardless if another one is already playing.)
> 
> I can play ONE wav file using sndio.
> 
> https://codeberg.org/pkw/siotest/src/branch/main/siotest.c#L130
> 
> What is the easiest and most idiomatic way
> to play multiples ones ?
> 
> My naive approach is to just do the same thing
> as I would do for one and put that into
> a pthread.  That means I am opening the 
> sndio device each time.  (sio_open)

That would work for 2-3 files, but would consume a lot of resources
and the offset between the files is difficult to control.

> 
> I see in game programming people do "mixing"
> of sound. 
> 

This is the most flexible approach, imo. In a loop "pull" a block of
data and send it to the device. In pseudo-code:

        while (1) {
                for (f = file_list; f != NULL; f = f->next) {
                        read_samples(f, tmp_buf, par.round);
                        mix_samples(out_buf, tmp_buf, par.round);
                }
                sio_write(hdl, out_buf, par.round * par.pchan * par.bps);
        }

If all files use the same format, the code can be small and
simple. Mixing is roughly adding the samples. It's even simpler if
they are small and are pre-loaded in memory.

Above approach can be extended naturally, ex. if conversions or
effects are necessary, they can be hidden in read_file(). If low
latency is needed, the file-system calls could go in a dedicated
thread, etc.

> Any pointers or places to look?
>

The playrec_cycle() function in src/usr.bin/aucat/aucat.c does this,
you can ignore the recording part and the conversions. Many programs
do something equivalent, so pick the one that's the most readable for
you.

> I want to use just OpenBSD and sndio if possible.
> I am using libsndfile, but that is just to
> open the wav files easily.
>