portaudio/doc/src/tutorial/querying_devices.dox

/** @page querying_devices Enumerating and Querying PortAudio Devices
@ingroup tutorial

@section tut_query1 Querying Devices

It is often fine to use the default device as we did previously in this tutorial, but there are times when you'll want to explicitly choose the device from a list of available devices on the system. To see a working example of this, check out pa_devs.c in the tests/ directory of the PortAudio source code. To do so, you'll need to first initialize PortAudio and Query for the number of Devices:

@code
    int numDevices;

    numDevices = Pa_GetDeviceCount();
    if( numDevices < 0 )
    {
        printf( "ERROR: Pa_CountDevices returned 0x%x\n", numDevices );
        err = numDevices;
        goto error;
    }
@endcode


If you want to get information about each device, simply loop through as follows:

@code
    const   PaDeviceInfo *deviceInfo;

    for( i=0; i<numDevices; i++ )
    {
        deviceInfo = Pa_GetDeviceInfo( i );
        ...
    }
@endcode

The Pa_DeviceInfo structure contains a wealth of information such as the name of the devices, the default latency associated with the devices and more. The structure has the following fields:

@code
int 	structVersion
const char * 	name
PaHostApiIndex 	hostApi
int 	maxInputChannels
int 	maxOutputChannels
PaTime 	defaultLowInputLatency
PaTime 	defaultLowOutputLatency
PaTime 	defaultHighInputLatency
PaTime 	defaultHighOutputLatency
double 	defaultSampleRate
@endcode

You may notice that you can't determine, from this information alone, whether or not a particular sample rate is supported. This is because some devices support ranges of sample rates, others support, a list of sample rates, and still others support some sample rates and number of channels combinations but not others. To get around this, PortAudio offers a function for testing a particular device with a given format:

@code
    const PaStreamParameters *inputParameters;
    const PaStreamParameters *outputParameters;
    double desiredSampleRate;
    ...
    PaError err;

    err = Pa_IsFormatSupported( inputParameters, outputParameters, desiredSampleRate );
    if( err == paFormatIsSupported )
    {
       printf( "Hooray!\n");
    }
    else
    {
       printf("Too Bad.\n");
    }
@endcode

Filling in the inputParameters and outputParameters fields is shown in a moment.

Once you've found a configuration you like, or one you'd like to go ahead and try, you can open the stream by filling in the PaStreamParameters structures, and calling Pa_OpenStream:

@code
    double srate = ... ;
    PaStream *stream;
    unsigned long framesPerBuffer = ... ; //could be paFramesPerBufferUnspecified, in which case PortAudio will do its best to manage it for you, but, on some platforms, the framesPerBuffer will change in each call to the callback
    PaStreamParameters outputParameters;
    PaStreamParameters inputParameters;

    bzero( &inputParameters, sizeof( inputParameters ) ); //not necessary if you are filling in all the fields
    inputParameters.channelCount = inChan;
    inputParameters.device = inDevNum;
    inputParameters.hostApiSpecificStreamInfo = NULL;
    inputParameters.sampleFormat = paFloat32;
    inputParameters.suggestedLatency = Pa_GetDeviceInfo(inDevNum)->defaultLowInputLatency ;
    inputParameters.hostApiSpecificStreamInfo = NULL; //See you specific host's API docs for info on using this field


    bzero( &outputParameters, sizeof( outputParameters ) ); //not necessary if you are filling in all the fields
    outputParameters.channelCount = outChan;
    outputParameters.device = outDevNum;
    outputParameters.hostApiSpecificStreamInfo = NULL;
    outputParameters.sampleFormat = paFloat32;
    outputParameters.suggestedLatency = Pa_GetDeviceInfo(outDevNum)->defaultLowOutputLatency ;
    outputParameters.hostApiSpecificStreamInfo = NULL; //See you specific host's API docs for info on using this field

    err = Pa_OpenStream(
                    &stream,
                    &inputParameters,
                    &outputParameters,
                    srate,
                    framesPerBuffer,
                    paNoFlag, //flags that can be used to define dither, clip settings and more
                    portAudioCallback, //your callback function
                    (void *)this ); //data to be passed to callback. In C++, it is frequently (void *)this
    //don't forget to check errors!
@endcode


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