CODEWITHSUNDEEP
portaudio
user2870035
user2870035

Reputation: 21

Configuring multiple devices in PortAudio: Invalid device error

This query is regarding the Portaudio framework. A little background before I ask the question:I am working on an application in PortAudio to output audio through a multichannel(=8) device. However, the device I am using does not expose itself as a single 8-channel device but instead shows up in my device-list as 4 stereo devices. On searching for an approach to handle this, I got to know that WinMME in PortAudio supports multiple devices.

Now, I went through the appropriate header file("pa_win_wmme.h") and followed the suggestions present. But I get the 'Invalid device' error (error number -9996) after calling PA_OpenStream(). In the above mentioned header file, they have in fact specified the right parameter(s) to use when configuring multiple devices to avoid this error, but in-spite of following them, I still get the error. So I wanted to know if anybody has faced a similar issue and whether I have missed/wrongly configured anything.

I am pasting the required snippets of code below for reference:

PaStreamParameters outputParameters;
PaWinMmeStreamInfo wmmeStreamInfo;
PaWinMmeDeviceAndChannelCount wmmeDeviceAndNumChannels;**
...
...
outputParameters.device = paUseHostApiSpecificDeviceSpecification;
outputParameters.channelCount = 8;
outputParameters.sampleFormat = paFloat32; /* 32 bit floating point processing */
outputParameters.hostApiSpecificStreamInfo = NULL;

wmmeStreamInfo.size = sizeof(PaWinMmeStreamInfo);
wmmeStreamInfo.hostApiType = paMME; 
wmmeStreamInfo.version = 1;
wmmeStreamInfo.flags = paWinMmeUseMultipleDevices;
wmmeDeviceAndNumChannels.channelCount = 2;
wmmeDeviceAndNumChannels.device = 3;
wmmeStreamInfo.devices = &wmmeDeviceAndNumChannels;
wmmeStreamInfo.deviceCount = 4;
outputParameters.hostApiSpecificStreamInfo = &wmmeStreamInfo;

The device id = 3 was obtained through

Pa_GetHostApiInfo( Pa_HostApiTypeIdToHostApiIndex( paMME ) )->defaultOutputDevice

I hope I have made the query clear enough. Will be happy to provide more details if required.

Thanks.

Upvotes: 1

Views: 2774

Answers (2)

user2870035
user2870035

Reputation: 21

I finally figured out the mistake :-) The configuration for multiple devices must be made as an array. For instance, in the above case wmmeDeviceAndNumChannels must be an array of 4, with each individual device field containing the corresponding device index of each of the 4 stereo devices. The channelCount remains 2. The outputParameters.channelCount still has to be the aggregate number of channels, i.e. 8. With this I was able to run the application with a single stream, and of course, without any errors related to invalid device or invalid number of channels.:-)

Thanks.

Upvotes: 1

kevinvanleer
kevinvanleer

Reputation: 1125

Based on the code pasted above, it looks like you are trying to call open on a single 8-channel device. Instead you will have to get the Pa index of all four devices and call open 4 times. Once for each stereo device. You will then have 4 interleaved stereo streams to maintain. My guess is that changing channelCount = 8 to channelCount = 2 will allow the first stream to open.

Upvotes: 0

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