[PULL,15/26] audio: add mixeng option (documentation)
diff mbox series

Message ID 20190919083629.29998-16-kraxel@redhat.com
State New
Headers show
Series
  • [PULL,01/26] audio: api for mixeng code free backends
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Commit Message

Gerd Hoffmann Sept. 19, 2019, 8:36 a.m. UTC
From: Kővágó, Zoltán <dirty.ice.hu@gmail.com>

This will allow us to disable mixeng when we use a decent backend.

Disabling mixeng have a few advantages:
* we no longer convert the audio output from one format to another, when
  the underlying audio system would just convert it to a third format.
  We no longer convert, only the underlying system, when needed.
* the underlying system probably has better resampling and sample format
  converting methods anyway...
* we may support formats that the mixeng currently does not support (S24
  or float samples, more than two channels)
* when using an audio server (like pulseaudio) different sound card
  outputs will show up as separate streams, even if we use only one
  backend

Disadvantages:
* audio capturing no longer works (wavcapture, and vnc audio extension)
* some backends only support a single playback stream or very picky
  about the audio format.  In this case we can't disable mixeng.

However mixeng is not removed, only made optional, so this shouldn't be
a big concern.

Signed-off-by: Kővágó, Zoltán <DirtY.iCE.hu@gmail.com>
Message-id: b1a5c621da034c8b8485c9b2097080b9760f274a.1568574965.git.DirtY.iCE.hu@gmail.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 qapi/audio.json | 5 +++++
 qemu-options.hx | 6 ++++++
 2 files changed, 11 insertions(+)

Comments

Eric Blake Sept. 19, 2019, 3:27 p.m. UTC | #1
On 9/19/19 3:36 AM, Gerd Hoffmann wrote:
> From: Kővágó, Zoltán <dirty.ice.hu@gmail.com>
> 
> This will allow us to disable mixeng when we use a decent backend.
> 
> Disabling mixeng have a few advantages:
> * we no longer convert the audio output from one format to another, when
>   the underlying audio system would just convert it to a third format.
>   We no longer convert, only the underlying system, when needed.
> * the underlying system probably has better resampling and sample format
>   converting methods anyway...
> * we may support formats that the mixeng currently does not support (S24
>   or float samples, more than two channels)
> * when using an audio server (like pulseaudio) different sound card
>   outputs will show up as separate streams, even if we use only one
>   backend
> 
> Disadvantages:
> * audio capturing no longer works (wavcapture, and vnc audio extension)
> * some backends only support a single playback stream or very picky
>   about the audio format.  In this case we can't disable mixeng.
> 
> However mixeng is not removed, only made optional, so this shouldn't be
> a big concern.
> 

> +++ b/qemu-options.hx
> @@ -433,6 +433,7 @@ DEF("audiodev", HAS_ARG, QEMU_OPTION_audiodev,
>      "                specifies the audio backend to use\n"
>      "                id= identifier of the backend\n"
>      "                timer-period= timer period in microseconds\n"
> +    "                in|out.mixing-engineeng= use mixing engine to mix streams inside QEMU\n"

s/engineeng/engine/

Patch
diff mbox series

diff --git a/qapi/audio.json b/qapi/audio.json
index 9fefdf5186dd..0535eff7948f 100644
--- a/qapi/audio.json
+++ b/qapi/audio.json
@@ -11,6 +11,10 @@ 
 # General audio backend options that are used for both playback and
 # recording.
 #
+# @mixing-engine: use QEMU's mixing engine to mix all streams inside QEMU. When
+#                 set to off, fixed-settings must be also off. Not every backend
+#                 compatible with the off setting (default on, since 4.2)
+#
 # @fixed-settings: use fixed settings for host input/output. When off,
 #                  frequency, channels and format must not be
 #                  specified (default true)
@@ -31,6 +35,7 @@ 
 ##
 { 'struct': 'AudiodevPerDirectionOptions',
   'data': {
+    '*mixing-engine':  'bool',
     '*fixed-settings': 'bool',
     '*frequency':      'uint32',
     '*channels':       'uint32',
diff --git a/qemu-options.hx b/qemu-options.hx
index bbfd936d29ec..734a3b5d6569 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -433,6 +433,7 @@  DEF("audiodev", HAS_ARG, QEMU_OPTION_audiodev,
     "                specifies the audio backend to use\n"
     "                id= identifier of the backend\n"
     "                timer-period= timer period in microseconds\n"
+    "                in|out.mixing-engineeng= use mixing engine to mix streams inside QEMU\n"
     "                in|out.fixed-settings= use fixed settings for host audio\n"
     "                in|out.frequency= frequency to use with fixed settings\n"
     "                in|out.channels= number of channels to use with fixed settings\n"
@@ -503,6 +504,11 @@  Identifies the audio backend.
 Sets the timer @var{period} used by the audio subsystem in microseconds.
 Default is 10000 (10 ms).
 
+@item in|out.mixing-engine=on|off
+Use QEMU's mixing engine to mix all streams inside QEMU.  When off,
+@var{fixed-settings} must be off too.  Not every backend is fully
+compatible with the off setting.  Default is on.
+
 @item in|out.fixed-settings=on|off
 Use fixed settings for host audio.  When off, it will change based on
 how the guest opens the sound card.  In this case you must not specify