Re: Audio playback speed issue on sam460ex and pegasos2

[Volker Rümelin]

Am 29.03.23 um 21:20 schrieb BALATON Zoltan:
> On Tue, 28 Mar 2023, Volker Rümelin wrote:
> > it seems your Mac uses a 48kHz sample rate, although QEMU requested a 
> > 44.1kHz sample rate. Could you add -audiodev 
> > coreaudio,id=audio0,out.frequency=48000 to your command line and test 
> > if the playback speed and pitch is now correct?
>
> I guess you could also set the sampling rate in the guest to match the 
> host but if that results it to do resampling then it may use more CPU 
> that way.

With default settings QEMU resamples the selected guest rate to 
out.frequency.

> > The default for out.frequency is 44100.
>
> I think ALSA and Pulseaudio may also default to 48kHz. I remember 
> configuring ALSA to 44.1 kHz on my machine to avoid resampling in the 
> more common case of playing music. So is this a general problem or 
> something with the coreadio backend? Should this somehow detect the 
> host sampling rate and do something about it?

Querying the host sample rate and using the host sample rate instead of 
out.frequency seems easy. It gets difficult when someone changes the 
host sample rate when QEMU is running. Current QEMU code can't change 
the sample rate for an established audio stream. I think the Google 
Android emulator fork of QEMU uses the Core Audio API to resample the 
audio stream in this case.

> Regards,
> BALATON Zoltan