Re: [Qemu-devel] [PATCH] pulseaudio: reduce 24s recording latency

[Volker Rümelin]

Am 12.09.2015 um 16:35 schrieb Kővágó Zoltán:
> 2015-09-12 13:23 keltezéssel, Volker Rümelin írta:
> > On start up qemu opens a connection to pulseaudio in function
> > qpa_init_in and pulseaudio immediately starts recording to the 4MB
> > ringbuffer. The qemu guest, Windows 8.1 in my case, doesn't consume that
> > data if there is no process listening on the audio interface. Now if the
> > guest starts recording, it will see audio data which was recorded 24s 
> > ago.
>
> Weird, pulseaudio shouldn't delay the input more than 2 seconds in the 
> default config.  Maybe PA_STREAM_EARLY_REQUESTS help.  See my patch at 
> [1].  Alternatively we should maybe call pa_stream_flush when enabling 
> the input to tell pulseaudio to drop previously recorded samples.
>
> [1]: https://lists.gnu.org/archive/html/qemu-devel/2015-08/msg02455.html

Hi Zoltan,

I tested your suggestions.

There was the same 24s latency when I replaced PA_STREAM_ADJUST_LATENCY 
with PA_STREAM_EARLY_REQUESTS in function pa_stream_connect_record. This 
was to be expected, because the pulseaudio documentation only mentions 
playback there.

A call to pa_stream_flush in qpa_ctl_in in case VOICE_ENABLE: also 
didn't solve the problem.

But when I replaced pa_stream_flush with a repeated call to 
pa_stream_peek and pa_stream_drop things started to improve. Now I 
experience the 1-2s recording latency mentioned in the pulseaudio 
documentation. But this is still much higher than the latency I see with 
my old patch.

Regards,
Volker