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From: =?UTF-8?Q?Volker_R=c3=bcmelin?= <vr_qemu@t-online.de>
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Date: Sat, 12 Sep 2015 21:55:44 +0200
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Subject: Re: [Qemu-devel] [PATCH] pulseaudio: reduce 24s recording latency
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To: =?UTF-8?B?S8WRdsOhZ8OzIFpvbHTDoW4=?= <dirty.ice.hu@gmail.com>
Cc: =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= <marcandre.lureau@gmail.com>, QEMU <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>

Am 12.09.2015 um 16:35 schrieb K=C5=91v=C3=A1g=C3=B3 Zolt=C3=A1n:
> 2015-09-12 13:23 keltez=C3=A9ssel, Volker R=C3=BCmelin =C3=ADrta:
>>
>> 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 th=
at
>> data if there is no process listening on the audio interface. Now if t=
he
>> guest starts recording, it will see audio data which was recorded 24s=20
>> ago.
>
> Weird, pulseaudio shouldn't delay the input more than 2 seconds in the=20
> default config.  Maybe PA_STREAM_EARLY_REQUESTS help.  See my patch at=20
> [1].  Alternatively we should maybe call pa_stream_flush when enabling=20
> the input to tell pulseaudio to drop previously recorded samples.
>
> [1]: https://lists.gnu.org/archive/html/qemu-devel/2015-08/msg02455.htm=
l
>

Hi Zoltan,

I tested your suggestions.

There was the same 24s latency when I replaced PA_STREAM_ADJUST_LATENCY=20
with PA_STREAM_EARLY_REQUESTS in function pa_stream_connect_record. This=20
was to be expected, because the pulseaudio documentation only mentions=20
playback there.

A call to pa_stream_flush in qpa_ctl_in in case VOICE_ENABLE: also=20
didn't solve the problem.

But when I replaced pa_stream_flush with a repeated call to=20
pa_stream_peek and pa_stream_drop things started to improve. Now I=20
experience the 1-2s recording latency mentioned in the pulseaudio=20
documentation. But this is still much higher than the latency I see with=20
my old patch.

Regards,
Volker