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[PULL 04/13] audio: add mixing-engine option (documentation)
From: |
Gerd Hoffmann |
Subject: |
[PULL 04/13] audio: add mixing-engine option (documentation) |
Date: |
Fri, 18 Oct 2019 09:41:35 +0200 |
From: Kővágó, Zoltán <address@hidden>
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.
Originally thw two main use cases of the disabled option was: using
unsupported audio formats (5.1 and 7.1 audio) and having different
pulseaudio streams per audio frontend. Since we can have multiple
-audiodevs, the latter is not that important, so currently you only need
this option if you want to use 5.1 or 7.1 audio (implemented in a later
patch), otherwise it's probably better to stick to the old and tried
mixeng, since it's less picky about the backends.
The ideal solution would be to port as much as possible to gstreamer,
but this is currently out of scope:
https://wiki.qemu.org/Internships/ProjectIdeas/AudioGStreamer
Signed-off-by: Kővágó, Zoltán <address@hidden>
Message-id: address@hidden
Signed-off-by: Gerd Hoffmann <address@hidden>
---
qapi/audio.json | 6 ++++++
qemu-options.hx | 15 +++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/qapi/audio.json b/qapi/audio.json
index e45218f081f2..83312b23391e 100644
--- a/qapi/audio.json
+++ b/qapi/audio.json
@@ -11,6 +11,11 @@
# 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 and
+# convert audio formats when not supported by the backend. When
+# set to off, fixed-settings must be also off (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 +36,7 @@
##
{ 'struct': 'AudiodevPerDirectionOptions',
'data': {
+ '*mixing-engine': 'bool',
'*fixed-settings': 'bool',
'*frequency': 'uint32',
'*channels': 'uint32',
diff --git a/qemu-options.hx b/qemu-options.hx
index 793d70ff9388..996b6fba7461 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-engine= 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"
@@ -493,6 +494,10 @@ output's property with @code{out.@var{prop}}. For example:
-audiodev alsa,id=example,out.channels=1 # leaves in.channels unspecified
@end example
+NOTE: parameter validation is known to be incomplete, in many cases
+specifying an invalid option causes QEMU to print an error message and
+continue emulation without sound.
+
Valid global options are:
@table @option
@@ -503,6 +508,16 @@ 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 and convert
+audio formats when not supported by the backend. When off,
+@var{fixed-settings} must be off too. Note that disabling this option
+means that the selected backend must support multiple streams and the
+audio formats used by the virtual cards, otherwise you'll get no sound.
+It's not recommended to disable this option unless you want to use 5.1
+or 7.1 audio, as mixing engine only supports mono and stereo audio.
+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
--
2.18.1
- [PULL 00/13] Audio 20191018 patches, Gerd Hoffmann, 2019/10/18
- [PULL 01/13] audio: fix parameter dereference before NULL check, Gerd Hoffmann, 2019/10/18
- [PULL 03/13] audio: paaudio: ability to specify stream name, Gerd Hoffmann, 2019/10/18
- [PULL 13/13] paaudio: fix channel order for usb-audio 5.1 and 7.1 streams, Gerd Hoffmann, 2019/10/18
- [PULL 07/13] audio: support more than two channels in volume setting, Gerd Hoffmann, 2019/10/18
- [PULL 12/13] usbaudio: change playback counters to 64 bit, Gerd Hoffmann, 2019/10/18
- [PULL 09/13] audio: basic support for multichannel audio, Gerd Hoffmann, 2019/10/18
- [PULL 08/13] audio: replace shift in audio_pcm_info with bytes_per_frame, Gerd Hoffmann, 2019/10/18
- [PULL 10/13] usb-audio: do not count on avail bytes actually available, Gerd Hoffmann, 2019/10/18
- [PULL 04/13] audio: add mixing-engine option (documentation),
Gerd Hoffmann <=
- [PULL 05/13] audio: make mixeng optional, Gerd Hoffmann, 2019/10/18
- [PULL 11/13] usb-audio: support more than two channels of audio, Gerd Hoffmann, 2019/10/18
- [PULL 06/13] paaudio: get/put_buffer functions, Gerd Hoffmann, 2019/10/18
- [PULL 02/13] audio: paaudio: fix connection and stream name, Gerd Hoffmann, 2019/10/18
- Re: [PULL 00/13] Audio 20191018 patches, Peter Maydell, 2019/10/18