Enable platform-specific features from PortAudio about python-sounddevice HOT 8 OPEN

One possible feature would be the "exclusive mode" of WASAPI, see http://stackoverflow.com/questions/31306010/how-to-enable-wasapi-exclusive-mode-in-pyaudio

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PaAlsa_EnableRealtimeScheduling might be interesting for ALSA: http://portaudio.com/docs/v19-doxydocs-dev/pa__linux__alsa_8h.html#accc41e7fd89dc0a6163d54a4f25fb242

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It would be interesting to be able to select arbitrary channels for input and output. On Windows this is needed with ASIO. If you currently want to send data to output channels 9 and 10, you have to send data to all channels below 11. This means that sharing the soundcard with other applications becomes impossible.

The hostapis WDM-KS, MME, Directsound, normally only present 2 channels so it is not a problem there.

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@raecke I created an experimental implementation in #34. Can you please check if it works for you and leave a comment there?

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There is also PaAlsa_SetNumPeriods, which is by default set to 4, which seems random:

By default the number of periods is 4, this is the lowest number of periods that works well on the author's soundcard.

http://portaudio.com/docs/v19-doxydocs-dev/pa__linux__alsa_8h.html#a76f60d6f1ba6a298c038a9f3a6dccc53

It looks like this has to be called before opening a stream.

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OK, I'm trying to make an exhaustive list of the current host-API-specific settings, let's see if that works:

hostApiSpecificStreamInfo to be specified separately for the input and output device when creating a stream:

• PaAlsaStreamInfo::deviceString, only works if device index is set to paUseHostApiSpecificDeviceSpecification (a.k.a. -2)
• PaAsioStreamInfo::channelSelectors, needs PaAsioStreamInfo::flags to contain paAsioUseChannelSelectors
• PaMacCoreStreamInfo::channelMap, can be set with PaMacCore_SetupChannelMap
• PaMacCoreStreamInfo::flags, paMacCoreChangeDeviceParameters, paMacCoreFailIfConversionRequired, paMacCoreConversionQuality*, ...
• PaWinDirectSoundStreamInfo::channelMask, needs paWinDirectSoundUseChannelMask flag
• PaWinDirectSoundStreamInfo::framesPerBuffer, needs paWinDirectSoundUseLowLevelLatencyParameters flag
• PaWasapiStreamInfo::channelMask, needs paWinWasapiUseChannelMask flag
• PaWasapiStreamInfo::flags, paWinWasapiExclusive, paWinWasapiPolling
• PaWasapiStreamInfo::hostProcessorOutput, needs paWinWasapiRedirectHostProcessor flag, separate callback instead of "normal" audio callback?
• PaWasapiStreamInfo::hostProcessorInput
• PaWasapiStreamInfo::threadPriority, needs paWinWasapiThreadPriority flag, cannot be different for input and output!
• PaWasapiStreamInfo::streamCategory
• PaWasapiStreamInfo::streamOption
• PaWDMKSSpecificStreamInfo::input ???
• PaWDMKSSpecificStreamInfo::output ???
• PaWinWDMKSInfo::channelMask ???
• PaWinWDMKSInfo::flags ???
• PaWinMmeStreamInfo::framesPerBuffer
• PaWinMmeStreamInfo::bufferCount
• PaWinMmeStreamInfo::devices, needs paWinMmeUseMultipleDevices flag
• PaWinMmeStreamInfo::channelMask, needs paWinMmeUseChannelMask flag
• PaWinMmeStreamInfo::flags: paWinMmeDontThrottleOverloadedProcessingThread, paWinMmeWaveFormatDolbyAc3Spdif, paWinMmeWaveFormatWmaSpdif

Functions that are called with a stream pointer:

• PaAlsa_EnableRealtimeScheduling
• PaAlsa_GetStreamInputCard
• PaAlsa_GetStreamOutputCard
• PaAsio_SetStreamSampleRate
• PaMacCore_GetStreamInputDevice
• PaMacCore_GetStreamOutputDevice
• PaWasapi_GetFramesPerHostBuffer, for use with PaWasapiHostProcessorCallback
• PaWinMME_GetStreamInputHandle
• PaWinMME_GetStreamOutputHandle

Global functions:

• PaAlsa_SetNumPeriods
• PaAlsa_SetRetriesBusy
• PaAlsa_SetLibraryPathName Does this work with the way we are loading the library?
• PaAsio_GetAvailableBufferSizes, takes the device index
• PaAsio_ShowControlPanel, takes the device index and "the calling application's main window handle", does this work in Python?
• PaAsio_GetInputChannelName, takes the device index
• PaAsio_GetOutputChannelName, takes the device index
• PaJack_SetClientName, must be called before Pa_Initialize!
• PaJack_GetClientName
• PaMacCore_GetChannelName, takes device and channel index
• PaMacCore_GetBufferSizeRange, takes device index
• PaWasapi_GetDeviceDefaultFormat, takes device index
• PaWasapi_GetDeviceRole, takes device index
• PaWasapi_ThreadPriorityBoost, for blocking interface only
• PaWasapi_ThreadPriorityRevert
• PaWasapi_GetJackCount, takes device index
• PaWasapi_GetJackDescription, takes device index
• PaWasapi_IsLoopback (will be in PortAudio 19.8), takes device index

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Would love to be able to fetch PaAsio_GetInputChannelName and PaAsio_GetOutputChannelName though it looks like there hasn't been much movement on this feature?

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@philipmountifield Can you please create a new issue with your request, including a suggestion how the new API should look like?

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