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My main goal at the moment is to get detailed information about all of the local machine's Audio Endpoint Devices. That is the objects representing the audio peripherals. I want to be able to choose which device to record from based on some logic (or eventually allow the user to manually do so).

Here's what I've got so far. I'm pretty new to c++ so dealing with all of these abstract classes is getting a bit tricky so feel free to comment on code quality as well.

//Create vector of IMMDevices
UINT endpointCount = NULL;
(*pCollection).GetCount(&endpointCount);
std::vector<IMMDevice**> IMMDevicePP;   //IMMDevice seems to contain all endpoint devices, so why have a collection here?
for (UINT i = 0; i < (endpointCount); i++)
{
IMMDevice* pp = NULL;
(*pCollection).Item(i, &pp);
IMMDevicePP.assign(1, &pp);
}

My more technical goal at present is to get objects that implement this interface: http://msdn.microsoft.com/en-us/library/windows/desktop/dd371414(v=vs.85).aspx This is a type that is supposed to represent a single Audio Endpoint device whereas the IMMDevice seems to contain a collection of devices. However IMMEndpoint only contains a method called GetDataFlow so I'm unsure if that will help me. Again the goal is to easily select which endpoint device to record and stream audio from.

Any suggestions? Am I using the wrong API? This API definitely has good commands for the actual streaming and sampling of the audio but I'm a bit lost as to how to make sure I'm using the desired device.

lonious
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2 Answers2

4

WASAPI will allow you to do what you need so you're using the right API. You're mistaken about IMMDevice representing a collection of audio devices though, that is IMMDeviceCollection. IMMDevice represents a single audio device. By "device", WASAPI does't mean audio card as you might expect, rather it means a single input/output on such card. For example an audio card with analog in/out + digital out will show up as 3 IMMDevices each with it's own IMMEndpoint. I'm not sure what detailed info you're after but it seems to me IMMDevice will provide you with everything you need. Basically, you'll want to do something like this:

  • Create an IMMDeviceEnumerator
  • Call EnumAudioEndpoints specifying render, capture or both, to enumerate into an IMMDeviceCollection
  • Obtain individual IMMDevice instances from IMMDeviceCollection
  • Device name and description can be queried from IMMDevice using OpenPropertyStore (http://msdn.microsoft.com/en-us/library/windows/desktop/dd370812%28v=vs.85%29.aspx). Additional supported device details can be found here: http://msdn.microsoft.com/en-us/library/windows/desktop/dd370794%28v=vs.85%29.aspx.
  • IMMDevice instances obtained from IMMDeviceCollection will also be instances of IMMEndpoint, use QueryInterface to switch between the two. However, as you noted, this will only tell you if you've got your hands on a render or capture device. Much easier to only ask for what you want directly on EnumAudioEndpoints.
  • About code quality: use x->f() instead if (*x).f(), although it's technically the same thing the -> operator is the common way to call a function through an object pointer
  • Don't use vector::assign, apparently that replaces the contents of the entire vector on each call so you'll end up with a collection of size 1 regardless of the number of available devices. Use push_back instead.
Sjoerd van Kreel
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  • I've narrowed the type down to `PROPVARIANT` for each `IMMDEVICE` but now I'm not sure how to sift through this gigantic structure to find something useful about my device. Here's the doc: http://msdn.microsoft.com/en-us/library/windows/desktop/aa380072(v=vs.85).aspx Could you possibly enlighten me as to the meaning of all of these members of PROPVARIANT? – lonious Oct 01 '14 at 08:04
2

After enumerating your IMMDevices as Sjoerd stated it is a must to retrieve the IPropertyStore information for the device. From there you have to extract the PROPVARIANT object as such:

PROPERTYKEY key;
HRESULT keyResult = (*IMMDeviceProperties[i]).GetAt(p, &key);

then

PROPVARIANT propVari;
HRESULT propVariResult = (*IMMDeviceProperties[i]).GetValue(key, &propVari);

according to these documents:

http://msdn.microsoft.com/en-us/library/windows/desktop/bb761471(v=vs.85).aspx http://msdn.microsoft.com/en-us/library/windows/desktop/aa380072(v=vs.85).aspx

And finally to navigate the large PROPVARIANT structure in order to get the friendly name of the audio endpoint device simply access the pwszVal member of the PROPVARIANT structure as illustrated here:

http://msdn.microsoft.com/en-us/library/windows/desktop/dd316594(v=vs.85).aspx

All about finding the right documentation!

lonious
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