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

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> 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).

In fact, the qapi generator had special code to detect and reject
#optional tags for some six months (from commit 1d8bda128d2 to
67ab1ce9263), just to ensure patches in flight don't add them.  This one
has been in flight for even longer.

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