C#: Unity3D and NAudio EnumerateAudioEndPoints throws NullReferenceException

system · February 17, 2012, 6:47am

I’m trying to use the NAudio library in a Unity3D project. When calling MMDeviceEnumerator.EnumerateAudioEndPoints, a NullReferenceException is thrown. This does not occur in a Visual Studio project targeting .NET 2.0. The enumerator itself is not null. That method wraps a call to IMMDeviceEnumerator.EnumAudioEndpoints, which is what’s directly throwing this exception (I moved a bunch of code from NAudio into my Unity3D project).

The only real difference here is that it’s running inside a Unity3D game, rather than a standard Visual Studio application. What could be causing this? Please help.

Update:

My code that throws (second line):

MMDeviceEnumerator enumerator = new MMDeviceEnumerator();
MMDeviceCollection collection = enumerator.EnumerateAudioEndPoints(DataFlow.All, DeviceState.All);

NAudio code that throws (second line of method):

public MMDeviceCollection EnumerateAudioEndPoints(DataFlow dataFlow, DeviceState dwStateMask)
{
    IMMDeviceCollection result;
    Marshal.ThrowExceptionForHR(_realEnumerator.EnumAudioEndpoints(dataFlow, dwStateMask, out result));
    return new MMDeviceCollection(result);
}

Update x2:

In the constructor for MMDeviceEnumerator in NAudio:

_realEnumerator = new MMDeviceEnumeratorComObject() as IMMDeviceEnumerator;

The new com object is not null, but when casting, it becomes null. Again, this works in a Visual Studio project, but not Unity3D. Here’s the definitions of each (from the NAudio source):

[ComImport, Guid("BCDE0395-E52F-467C-8E3D-C4579291692E")]
class MMDeviceEnumeratorComObject
{
}

and

[Guid("A95664D2-9614-4F35-A746-DE8DB63617E6"),
    InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IMMDeviceEnumerator
{
    int EnumAudioEndpoints(DataFlow dataFlow, DeviceState stateMask,
        out IMMDeviceCollection devices);
    
    int GetDefaultAudioEndpoint(DataFlow dataFlow, Role role, out IMMDevice endpoint);
    
    int GetDevice(string id, out IMMDevice deviceName);
    
    int RegisterEndpointNotificationCallback(IMMNotificationClient client);
    
    int UnregisterEndpointNotificationCallback(IMMNotificationClient client);
}

I can post the other objects in there if necessary. What I’m missing is probably the core “why” something between Unity3D (also targeting .NET 2.0) and Visual Studio would change.

matt-mccallus · July 8, 2016, 1:26am

I never was able to get around the problem I was having. I found that I needed to create a native C++ DLL to do this stuff, and I just load that DLL and call into it from the Unity (C#) application.

BCook99 · March 22, 2022, 7:39pm

Using a C++ DLL solved this issue for me. See here https://stackoverflow.com/questions/50722026/how-to-get-and-set-system-volume-in-windows

GeorgeUamTec · May 13, 2022, 1:57am

HI @BCook99,

I have ran in the same issue where I ran the NAudio in Visual studio using C#. However also need to run this in Unity which I have been challenged with and no result apart from NullReferenceException.

In my case I don’t want to control volume as the C++ DLL has demonstrated in the link example. I am trying to receive information on the Audio Mic device Name and ID which I can retrieve in the Visual Studio Project

I am not very familiar with C++ and building of DLL’s. In the example link. I don’t see what way in helping retrieve this important information

Here is an example image of a little app I built utilising Visual Studio and you can see the result I would like logged in Unity.

Any guidance would be great in achieving the same result