Re: [PATCH 06/23] sdlaudio: fill remaining sample buffer with silence

[Volker Rümelin]

> On 10/01/2021 11.02, Volker Rümelin wrote:
> > Fill the remaining sample buffer with silence. To fill it with
> > zeroes is wrong for unsigned samples because this is silence
> > with a DC bias.
> >
> > Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
> > ---
> >   audio/sdlaudio.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/audio/sdlaudio.c b/audio/sdlaudio.c
> > index 79eed23849..01ae4c600e 100644
> > --- a/audio/sdlaudio.c
> > +++ b/audio/sdlaudio.c
> > @@ -235,7 +235,8 @@ static void sdl_callback (void *opaque, Uint8 
> > *buf, int len)
> >         /* clear remaining buffer that we couldn't fill with data */
> >       if (len) {
> > -        memset(buf, 0, len);
> > +        audio_pcm_info_clear_buf(&hw->info, buf,
> > +                                 len / hw->info.bytes_per_frame);
> >       }
> >   }
>
> Ignorant question: Is anybody still using unsigned samples in the 21st 
> century?

Hi Thomas,

you are probably right that no one is knowingly using unsigned samples 
anymore. But qemu emulates audio devices from the last century. For 
example with the command line options -machine pcspk-audiodev=audio0 
-audiodev sdl,id=audio0,out.buffer-length=3750,out.mixing-engine=off you 
will see 8 bit unsigned samples in the SDL callback buffer.

With best regards,
Volker

> Anyway,
> Reviewed-by: Thomas Huth <thuth@redhat.com>