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| Notes about WDM-KS host API | |
| --------------------------- | |
| Status history | |
| -------------- | |
| 16th January 2011: | |
| Added support for WaveRT device API (Vista and later) for even lesser | |
| latency support. | |
| 10th November 2005: | |
| Made following changes: | |
| * OpenStream: Try all PaSampleFormats internally if the the chosen | |
| format is not supported natively. This fixed several problems | |
| with soundcards that did not take kindly to using 24-bit 3-byte formats. | |
| * OpenStream: Make the minimum framesPerHostIBuffer (and framesPerHostOBuffer) | |
| the default frameSize for the playback/recording pin. | |
| * ProcessingThread: Added a switch to only call PaUtil_EndBufferProcessing | |
| if the total input frames equals the total output frames | |
| 5th September 2004: | |
| This is the first public version of the code. It should be considered | |
| an alpha release with zero guarantee not to crash on any particular | |
| system. So far it has only been tested in the author's development | |
| environment, which means a Win2k/SP2 PIII laptop with integrated | |
| SoundMAX driver and USB Tascam US-428 compiled with both MinGW | |
| (GCC 3.3) and MSVC++6 using the MS DirectX 9 SDK. | |
| It has been most widely tested with the MinGW build, with most of the | |
| test programs (particularly paqa_devs and paqa_errs) passing. | |
| There are some notable failures: patest_out_underflow and both of the | |
| blocking I/O tests (as blocking I/O is not implemented). | |
| At this point the code needs to be tested with a much wider variety | |
| of configurations and feedback provided from testers regarding | |
| both working and failing cases. | |
| What is the WDM-KS host API? | |
| ---------------------------- | |
| PortAudio for Windows currently has 3 functional host implementations. | |
| MME uses the oldest Windows audio API which does not offer good | |
| play/record latency. | |
| DirectX improves this, but still imposes a penalty | |
| of 10s of milliseconds due to the system mixing of streams from | |
| multiple applications. | |
| ASIO offers very good latency, but requires special drivers which are | |
| not always available for cheaper audio hardware. Also, when ASIO | |
| drivers are available, they are not always so robust because they | |
| bypass all of the standardised Windows device driver architecture | |
| and hit the hardware their own way. | |
| Alternatively there are a couple of free (but closed source) ASIO | |
| implementations which connect to the lower level Windows | |
| "Kernel Streaming" API, but again these require special installation | |
| by the user, and can be limited in functionality or difficult to use. | |
| This is where the PortAudio "WDM-KS" host implementation comes in. | |
| It directly connects PortAudio to the same Kernel Streaming API which | |
| those ASIO bridges use. This avoids the mixing penalty of DirectX, | |
| giving at least as good latency as any ASIO driver, but it has the | |
| advantage of working with ANY Windows audio hardware which is available | |
| through the normal MME/DirectX routes without the user requiring | |
| any additional device drivers to be installed, and allowing all | |
| device selection to be done through the normal PortAudio API. | |
| Note that in general you should only be using this host API if your | |
| application has a real requirement for very low latency audio (<20ms), | |
| either because you are generating sounds in real-time based upon | |
| user input, or you a processing recorded audio in real time. | |
| The only thing to be aware of is that using the KS interface will | |
| block that device from being used by the rest of system through | |
| the higher level APIs, or conversely, if the system is using | |
| a device, the KS API will not be able to use it. MS recommend that | |
| you should keep the device open only when your application has focus. | |
| In PortAudio terms, this means having a stream Open on a WDMKS device. | |
| Usage | |
| ----- | |
| To add the WDMKS backend to your program which is already using | |
| PortAudio, you must define PA_USE_WDMKS=1 in your build file, | |
| and include the pa_win_wdmks\pa_win_wdmks.c into your build. | |
| The file should compile in both C and C++. | |
| You will need a DirectX SDK installed on your system for the | |
| ks.h and ksmedia.h header files. | |
| You will need to link to the system "setupapi" library. | |
| Note that if you use MinGW, you will get more warnings from | |
| the DX header files when using GCC(C), and still a few warnings | |
| with G++(CPP). | |