WASAPI-specific PortAudio API extension header discussion

[DJKero]

WASAPI Streams have some latency related and stream behaviour attributes to configure:

PaWasapiStreamInfo:
http://files.portaudio.com/docs/v19-doxydocs/structPaWasapiStreamInfo.html

• flags: http://files.portaudio.com/docs/v19-doxydocs/pa__win__wasapi_8h_source.html#l00057
• threadPriority: http://files.portaudio.com/docs/v19-doxydocs/pa__win__wasapi_8h_source.html#l00239
• streamCategory: http://files.portaudio.com/docs/v19-doxydocs/pa__win__wasapi_8h_source.html#l00275
• streamOption: http://files.portaudio.com/docs/v19-doxydocs/pa__win__wasapi_8h_source.html#l00298

threadPriority reference (if you find anything else please comment):
http://files.portaudio.com/docs/v19-doxydocs/pa__win__wasapi_8h.html#a561291b0188f6f29246ea669b48e2661

streamCategory reference:
https://docs.microsoft.com/en-us/windows/win32/api/audiosessiontypes/ne-audiosessiontypes-audio_stream_category

streamOption reference:
https://docs.microsoft.com/en-us/windows/win32/api/audioclient/ne-audioclient-audclnt_streamoptions

[DJKero]

I'm not sure, but it seems that the flag paWinWasapiThreadPriority allows you to set a custom threadPriority to the scheduler?

If so, here's the reference:
https://docs.microsoft.com/en-us/windows/win32/procthread/scheduling-priorities

[DJKero]

Seems to me that the lowest latency config would be:

flags:
paWinWasapiExclusive
paWinWasapiRedirectHostProcessor
paWinWasapiThreadPriority

threadPriority:
something high that works, if it's the same as windows scheduler 24~26 or 31

streamOption:
eStreamOptionRaw / eStreamOptionMatchFormat

[sebastian-heinz]

Added a flag to request for exclusive mode to a device:

lowl_audio/src/lowl_device.h

Line 28 in 558e5fb

virtual void set_exclusive_mode(bool p_exclusive_mode, Error &error) = 0;

Added code for setting exclusive mode flags for WASAPI:

lowl_audio/src/lowl_device_pa.cpp

Line 353 in 558e5fb

if (pa_api_info->type == paWASAPI) {

still need to implement for other drivers that are available in PA, that support some sort of performance setting for pro audio.

also need to validate if this code works, and perhaps adjust the parameter if required

note: it need to be set before starting the device

[sebastian-heinz]

wasapi is now implemented as a driver : #23
It will provide you a list of supported configurations for each device, by calling getProperties on a device.
https://github.com/sebastian-heinz/lowl_audio/blob/master/demo/main.cpp#L149

The same functionality is also intended for PortAudio, so instead of trying to find a working configuration, different sample rates will be probed and then exposed to the user, so it should be as easy as selecting a configuration that has exclusive mode available.

I will still keep it open for now as testing with port audio is not yet completed for this feature