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From: "Volker Rümelin" <vr_qemu@t-online.de>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: QEMU <qemu-devel@nongnu.org>, "Zoltán Kővágó" <dirty.ice.hu@gmail.com>
Subject: Re: [PATCH 03/23] sdlaudio: add -audiodev sdl, out.buffer-count option
Date: Sun, 31 Jan 2021 18:30:41 +0100
Message-ID: <872b13e9-36d9-1690-3b47-5943d9370164@t-online.de> (raw)
In-Reply-To: <20210114142756.ixa3qhqtwcyebl6a@sirius.home.kraxel.org>

>    Hi,
>
>> -    hw->samples = obt.samples;
>> +    hw->samples = (spdo->has_buffer_count ? spdo->buffer_count : 4) *
>> +        obt.samples;
>> +# @buffer-count: number of buffers (default 4)
> Any specific reason for this default?
>
> In my testing I've needed much higher values.
> 8 still got me crackling sound, 16 worked ok.

Hi Gerd,

this was an attempt to come up with SDL audio settings which work for 
all SDL audio drivers. Unfortunately, the different SDL audio drivers 
have different timings and there are no default settings that work for 
all of them. Here are two examples where buffer-count=4 works.

On my Linux system I use

export SDL_AUDIODRIVER=pulse
and start qemu with -device intel-hda -device hda-duplex,audiodev=audio0 
-machine pcspk-audiodev=audio0 -audiodev 
sdl,id=audio0,out.buffer-length=3750

Due to the mix-up of samples and frames in audio/sdlaudio.c the callback 
buffer has a size of 2 * 3.75ms = 7.5ms and SDL calls the callback 
function every 7.5ms. With out.buffer-count=4 that's a 4 * 7.5ms = 30ms 
buffer on the qemu side. This is larger than the minimum size of 
timer-period.

On Windows the timing is different. The time between SDL callback calls 
is a multiple of 10ms. I have to use

export SDL_AUDIODRIVER=directsound
and start qemu with -device intel-hda -device hda-duplex,audiodev=audio0 
-machine pcspk-audiodev=audio0 -audiodev 
sdl,id=audio0,timer-period=1000,out.buffer-length=5500

With the above settings the playback stream sometimes will see 2*10ms + 
1ms stalls. The qemu hda codec can barely handle this. On average it 
will drop playback data after 23.22ms.

With best regards,
Volker

> take care,
>    Gerd
>



  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-10 10:01 [PATCH 00/23] next round of audio patches Volker Rümelin
2021-01-10 10:02 ` [PATCH 01/23] sdlaudio: remove leftover SDL1.2 code Volker Rümelin
2021-01-14 15:28   ` Thomas Huth
2021-01-10 10:02 ` [PATCH 02/23] audio: fix bit-rotted code Volker Rümelin
2021-01-14 14:32   ` Gerd Hoffmann
2021-01-31 17:13     ` Volker Rümelin
2021-01-10 10:02 ` [PATCH 03/23] sdlaudio: add -audiodev sdl,out.buffer-count option Volker Rümelin
2021-01-14 14:27   ` [PATCH 03/23] sdlaudio: add -audiodev sdl, out.buffer-count option Gerd Hoffmann
2021-01-31 17:30     ` Volker Rümelin [this message]
2021-01-15  8:39   ` Markus Armbruster
2021-01-10 10:02 ` [PATCH 04/23] sdlaudio: don't start playback in init routine Volker Rümelin
2021-01-15  6:28   ` Thomas Huth
2021-01-10 10:02 ` [PATCH 05/23] sdlaudio: always clear the sample buffer Volker Rümelin
2021-01-15  6:31   ` Thomas Huth
2021-01-10 10:02 ` [PATCH 06/23] sdlaudio: fill remaining sample buffer with silence Volker Rümelin
2021-01-14 16:58   ` Thomas Huth
2021-01-17  9:41     ` Volker Rümelin
2021-01-10 10:02 ` [PATCH 07/23] sdlaudio: replace legacy functions with modern ones Volker Rümelin
2021-01-15  7:04   ` Thomas Huth
2021-01-10 10:02 ` [PATCH 08/23] audio: split pcm_ops function get_buffer_in Volker Rümelin
2021-01-10 10:02 ` [PATCH 09/23] sdlaudio: add recording functions Volker Rümelin
2021-01-10 10:02 ` [PATCH 10/23] audio: break generic buffer dependency on mixing-engine Volker Rümelin
2021-01-10 10:02 ` [PATCH 11/23] sdlaudio: enable (in|out).mixing-engine=off Volker Rümelin
2021-01-10 10:02 ` [PATCH 12/23] audio: remove remaining unused plive code Volker Rümelin
2021-01-10 10:02 ` [PATCH 13/23] paaudio: avoid to clip samples multiple times Volker Rümelin
2021-01-10 10:02 ` [PATCH 14/23] paaudio: wait for PA_STREAM_READY in qpa_write() Volker Rümelin
2021-01-10 10:02 ` [PATCH 15/23] paaudio: wait until the playback stream is ready Volker Rümelin
2021-01-10 10:02 ` [PATCH 16/23] paaudio: remove unneeded code Volker Rümelin
2021-01-10 10:02 ` [PATCH 17/23] paaudio: comment bugs in functions qpa_init_* Volker Rümelin
2021-01-10 10:02 ` [PATCH 18/23] paaudio: limit minreq to 75% of audio timer_rate Volker Rümelin
2021-01-10 10:02 ` [PATCH 19/23] paaudio: send recorded data in smaller chunks Volker Rümelin
2021-01-10 10:02 ` [PATCH 20/23] dsoundaudio: replace GetForegroundWindow() Volker Rümelin
2021-01-10 10:02 ` [PATCH 21/23] dsoundaudio: rename dsound_open() Volker Rümelin
2021-01-10 10:02 ` [PATCH 22/23] dsoundaudio: enable f32 audio sample format Volker Rümelin
2021-01-10 10:02 ` [PATCH 23/23] dsoundaudio: fix log message Volker Rümelin
2021-01-10 10:24 ` [PATCH 00/23] next round of audio patches no-reply
2021-01-10 23:09   ` Volker Rümelin
2021-01-14 14:36 ` Gerd Hoffmann

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