Re: qemu modifies host audio sample rate with coreaudio backend to 44.1khz on startup

[Volker Rümelin]

Am 24.03.23 um 13:04 schrieb Christian Schoenebeck:
> On Friday, March 24, 2023 8:54:35 AM CET Thomas Huth wrote:
> > On 23/03/2023 21.03, Frank Carmickle wrote:
> > > Greetings all,
> > >
> > > Every time a qemu instance is run, the host systems audio hardware sample rate 
> > > is set to 44.1khz. Is it possible to change this behavior, and if so, how?
> >    Hi,
> >
> > not sure if I've got the question right, and I'm not an expert when it comes
> > to QEMU audio, but I think you can set the playback frequency like this for
> > example:
> >
> >    qemu-system-x86_64 --audiodev alsa,id=a1,out.frequency=48000
> >
> > ... but seems like the QEMU documentation is really lacking here, so I might
> > be wrong. Maybe Christian, Gerd or Marc-André could correct me in that case
> > (now on CC:).
> By default host's audio backend is opened with audio parameters requested by
> guest. So if guest requests 44.1 kHz then host's audio system is opened with
> 44.1 kHz as well (if supported by host's audio system that is).

Hi Christian,

I have a small correction. Your description above is correct for 
in|out.fixed-settings=off or in|out.mixing-engine=off. This is not the 
default.

By default most audio backends open a 44100Hz, signed 16bit stereo audio 
stream. CoreAudio ignores stream format options and JACK Audio and Spice 
ignore stream format and sample rate options.

With best regards,
Volker

> By supplying out.frequency=x you can override host's sample rate, but as guest
> apparently requested 44.1 kHz before, guest would probably still use 44.1 kHz
> and QEMU would resample the audio stream to the requested host's sample rate.
>
> So the question is what you really want to achieve. Maybe it would be better
> to force guest using the desired sample rate instead.
>
> Best regards,
> Christian Schoenebeck