Re: [Qemu-devel] [PATCH v2 43/52] audio: add mixeng option (documentation)

[Eric Blake]

On 12/23/18 2:52 PM, Kővágó, Zoltán wrote:
> 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 <address@hidden>
> ---
>  qapi/audio.json | 5 +++++
>  qemu-options.hx | 6 ++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/qapi/audio.json b/qapi/audio.json
> index 56d8ce439f..180bf207a8 100644
> --- a/qapi/audio.json
> +++ b/qapi/audio.json
> @@ -184,6 +184,10 @@
>  #
>  # General audio backend options that are used for both playback and 
> recording.
>  #
> +# @mixeng: #optional use QEMU's mixing engine to mix all streams inside QEMU.

The #optional tag is no longer necessary (the docs generator figures it
out from the '*mixeng' name below).

> +#          When set to off, fixed-settings must be also off.  Not every 
> backend
> +#          compatible with the off setting (default on)

Missing a '(since 4.0)' tag.

> +#
>  # @fixed-settings: #optional use fixed settings for host input/output.  When
>  #                  off, frequency, channels and format must not be specified
>  #                  (default on)
> @@ -207,6 +211,7 @@
>  ##
>  { 'struct': 'AudiodevPerDirectionOptions',
>    'data': {
> +    '*mixeng':         'bool',
>      '*fixed-settings': 'bool',
>      '*frequency':      'int',
>      '*channels':       'int',


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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