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Subject: Re: [Qemu-devel] [PATCH] pulseaudio: reduce 24s recording latency
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To: =?UTF-8?Q?Volker_R=c3=bcmelin?= <vr_qemu@t-online.de>, =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= <marcandre.lureau@gmail.com>
Cc: QEMU <qemu-devel@nongnu.org>, Gerd Hoffmann <kraxel@redhat.com>

2015-09-12 13:23 keltezéssel, Volker Rümelin írta:
> Hi,
>
> Am 12.09.2015 um 01:22 schrieb Marc-André Lureau:
>
>>> Current code doesn't provide pulseaudio buffer attributes for
>>> recording. Without buffer attributes pulseaudio uses a default
>>> buffer of 4MB. 4MB is approximately 24s 16bit stereo audio
>>> data at 44.1kHz.
>> Why isn't the buffer processed as soon as some data is available?
>>
>>
>
> 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

Zoltan