[vlc-devel] [PATCH 4/5] wasapi: add 24bits support

[Thomas Guillem]

On Mon, Oct 28, 2019, at 10:01, Rémi Denis-Courmont wrote:
> Hi,
> 
> Patch 4 is triplicating in one aout what belongs in OS HAL and VLC encoders. Are you going to write an MPEG Audio encoder in WASAPI just because some devices only accept that, also?

If users are asking for it, yes, but it won't be top priority at all (unless there is huge use case suddenly).

I added 24bit support because the first sound card I tested for the wasapi exclusive work was only accepting 24bit.

> 
> Patch 5 is doing the opposite of what people want to use exclusive mode for: implicitly add VLC conversion filters instead of disabling them.

OK. Maybe, the "wasapi-exclusive" option should be a global option (can be handled by Windows and Mac, don't know for pulse). That way, we can disable all audio filtering if enabled.

Then, let's say the input is 16bit and the soundcard is 24bit. What should we done in that case ? I assumed that it would be always OK to convert up to 24bit. Maybe we can add an option to this "exclusive" mode to prevent any conversion.

> 
> I don't think either of them is a step in the right direction.
> 
> Le 28 octobre 2019 10:25:02 GMT+02:00, Thomas Guillem <thomas at gllm.fr> a écrit :
>> 
>> On Fri, Oct 25, 2019, at 18:15, Rémi Denis-Courmont wrote:
>>> Le perjantaina 25. lokakuuta 2019, 15.45.16 EEST Alexandre Janniaux a écrit :
>>>> Hi,
>>>> 
>>>> To be honest, when the main answer is "it was decided
>>>> decades ago", I do feel it's a great secret wisdom.
>>> That's not what I wrote, and that just means it's obvious enough that there's 
>>> no point reopening the topic.
>>> 
>>>> Thomas's patch seems to make sense though, as a lot of
>>>> audio softwares are implementing it. There are also
>>>> probably some different use cases for exclusive mode when
>>>> using VLC in a different use case than the home multimedia
>>>> player.
>>> I don't see how the patchset is useful. I've seen requests for PCM pass-
>>> through, which sort-of makes sense with a digital output, but that's not at 
>>> all what this patchset does.
>>> 
>>> PCM pass-through means that you set exclusive mode and force the DAC format to 
>>> match the sample rate, channel map of the decoded input, and pick the wire 
>>> sample format, practically signed 16-bits. This patch does almost the exact 
>>> opposite: negotiate the rate, map and bit depth.
>> 
>> My patch is good step toward this direction.
>> It will first try the input format, but fallback to other possible compatible format. We can use a 3 value options: disabled, FORCED, ON if format compatible.
>> The main problem is that VLC can insert audio-filter like time stretch that could alterate the audio/format.
>> 
>> > 
>>> -- 
>>> Реми Дёни-Курмон
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> 
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