On Fri, Sep 23, 2022 at 10:48 PM Volker Rümelin <vr_qemu@t-online.de> wrote:

> The calculation of the buffer size needed to store audio samples
> after resampling is wrong for audio recording. For audio recording
> sw->ratio is calculated as
>
> sw->ratio = frontend sample rate / backend sample rate.
>
> From this follows
>
> frontend samples = frontend sample rate / backend sample rate
>  * backend samples
> frontend samples = sw->ratio * backend samples
>
> In 2 of 3 places in the audio recording code where sw->ratio
> is used in a calculation to get the number of frontend frames,
> the calculation is wrong. Fix this. The 3rd formula in
> audio_pcm_sw_read() is correct.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/71
> Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
>

Would you mind adding the test to qtest?

lgtm
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>



> ---
>  audio/audio.c          | 2 +-
>  audio/audio_template.h | 4 ++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/audio/audio.c b/audio/audio.c
> index ba0c62b120..60c7472d37 100644
> --- a/audio/audio.c
> +++ b/audio/audio.c
> @@ -995,7 +995,7 @@ void AUD_set_active_in (SWVoiceIn *sw, int on)
>   */
>  static size_t audio_frontend_frames_in(SWVoiceIn *sw, size_t frames_in)
>  {
> -    return ((int64_t)frames_in << 32) / sw->ratio;
> +    return (int64_t)frames_in * sw->ratio >> 32;
>  }
>
>  static size_t audio_get_avail (SWVoiceIn *sw)
> diff --git a/audio/audio_template.h b/audio/audio_template.h
> index 7192b19e73..6a0337ac6b 100644
> --- a/audio/audio_template.h
> +++ b/audio/audio_template.h
> @@ -112,7 +112,11 @@ static int glue (audio_pcm_sw_alloc_resources_, TYPE)
> (SW *sw)
>          return 0;
>      }
>
> +#ifdef DAC
>      samples = ((int64_t) sw->HWBUF->size << 32) / sw->ratio;
> +#else
> +    samples = (int64_t)sw->HWBUF->size * sw->ratio >> 32;
> +#endif
>
>      sw->buf = audio_calloc(__func__, samples, sizeof(struct st_sample));
>      if (!sw->buf) {
> --
> 2.35.3
>
>
>

-- 
Marc-André Lureau