Re: [Call for testing] sound: Implement /dev/dsp as a router device

Hello Jakob,

Jakob Alvermark wrote:
> Hi,
> 
> 
> This is cool.
> 
> I did some quick testing.
> 
> Playing some audio and plugging in my USB-C headset the audio switches over
> to the headset and continues playing in the headset.
> 
> However, unplugging the headset does not seem to work fully. If I play
> something in chromium (a Youtube video for example), it stops.

See what I write below, it could be a similar issue. Also, does this
happen on other browsers, say, firefox?

> I tried playing an mp3 file using audio/mpg123, and when unplugging the
> headset I get this error:
> 
> [src/libout123/libout123.c:out123_play():746] error: Error in writing audio,
> wrote only -1 of 2304 (Invalid argument?)!
> main: [src/mpg123.c:play_frame():857] error: Deep trouble! Cannot flush to
> my output anymore!

I am not familiar with audio/mpg123, but the error message suggests that
the program exits upon a write() error. That is not really an issue of
sound(4), but that audio/mpg123 exits on the first write() error. mpv
for example, or mplayer as you said, do not have this problem.

My first guess would be that the error is generated during the
hot-unpluging, because in the time window between the device detach and
the switch to the new default device, write() will have failed since the
device stopped doing IO at this point. That is not wrong behavior on
sound(4)'s side though.

> On the other hand, multimedia/mplayer does work, switching seamlessly
> between the laptop speaker and headset.

Just to make sure, the switching is successful even during IO, right?

> 
> Jakob
> 
> On 2025-04-06 21:08, Christos Margiolis wrote:
> > I've been working on a patch [1] to re-implement /dev/dsp as a
> > router/virtual device. The commit message in the review explains all the
> > high-level details and reasons behind the patch. This is the first of a
> > series of patches I'm working on.
> > 
> > For regular users, the main functional difference is that with this
> > patch, /dev/dsp is an actual router device (like when using
> > virtual_oss), which means that we have hot-swapping (i.e., changing the
> > default device and routing audio to it during IO without needing to
> > close and re-open /dev/dsp) built into sound(4).
> > 
> > Feel free to test the patch and please let me know if there's anything
> > that breaks or could be improved. You can play around with it just by
> > recording/playing audio as you always do, try some hot-swaps,
> > hot-(un)plugs, and anything that can stress test it. Just make sure you
> > open /dev/dsp, which should be the default for most applications anyway.
> > 
> > Christos
> > 
> > [1] https://reviews.freebsd.org/D49216

Christos