Re: [Qemu-devel] [PATCH 16/25] audio: add mixeng option (documentation)

[Zoltán Kővágó]

On 2019-08-26 15:35, Eric Blake wrote:
> On 8/25/19 1:46 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 9fefdf5186..dc7f9cb1e2 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.
>>  #
>> +# @mixeng: 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)
>> +#
> 
> 'mixeng' looks like an accidental typo, when 3 words later is 'mixing'.
> Would 'mix-eng' or 'mix-engine' be more obvious?

I used the spelling used in audio/mixeng.c, if we treat it as a name
then it should be simply 'mixeng'.  However I agree that it might not be
too meaningful for users, so 'mixing-engine' would make more sense, even
though it's a bit longer.

> 
> 
>>  ##
>>  { 'struct': 'AudiodevPerDirectionOptions',
>>    'data': {
>> +    '*mixeng':         'bool',
>>      '*fixed-settings': 'bool',
> 
> And the very next member is an example that QAPI doesn't have to use
> abbreviations.
> 

Regards,
Zoltan