VCamNetSample

This solution contains a Media Foundation Virtual Camera Sample developed using .NET. It works only on Windows 11 thanks to the MFCreateVirtualCamera API.

It's a port of the same project written in C++ VCamSample: https://github.com/smourier/VCamSample and it's based on DirectN for all DirectX, WIC and Media Foundation interop.

There are two projects in the solution:

• VCamNetSampleSource: the Media Source that provides RGB32 and NV12 streaming samples.
• VCamNetSample: the "driver" application that does very little but calls MFCreateVirtualCamera.

To test the .NET virtual cam:

• Build in debug or release
• Go to the build output and register the media source (a COM object) with a command similar to this: regsvr32 VCamNetSampleSource.comhost.dll (you must run this as administrator, it' not possible to register a Virtual Camera media source in HKCU, only in HKLM since it will be loaded by multiple processes)
• Run the VCamNetSample app.
• Run for example the Windows Camera app or using a Web Browser ImageCapture API

You should now see something like this in the Windows Camera App

Something like this in Windows' Edge Web Browser, using this testing page: https://googlechrome.github.io/samples/image-capture/grab-frame-take-photo.html

Something like this in OBS (Video Capture Device):

Something like this in Teams, yes, this is your avatar :-)

Notes

• The media source uses Direct2D and DirectWrite to create images. It will then create Media Foundation samples from these. To create MF samples, it can use:
  • The GPU, if a Direct3D manager has been provided by the environment. This is the case of the Windows 11 camera app.
  • The CPU, if no Direct3D environment has been provided. In this case, the media source uses a WIC bitmap as a render target and it then copies the bits over to an MF sample. The ImageCapture API code embedded in Chrome or Edge, Teams, etc. is an example of such a D3D-less environment (but sometimes it uses Direct3D).
  • If you want to force CPU usage at all times, you can change the code in MediaStream::SetD3DManager and put the lines there in comment.
• The media source provides RGB32 and NV12 formats as most setups prefer the NV12 format. Samples are initially created as RGB32 (Direct2D) and converted to NV12. To convert the samples, the media source uses two ways:
  • The GPU, if a Direct3D manager has been provided, using Media Foundation's Video Processor MFT.
  • The CPU, if no Direct3D environment has been provided. In this case, the RGB to NV12 conversion is done using Media Foundation's Color Converter DSP.
  • If you want to force RGB32 mode, you can change the code in MediaStream constructor and set the media types array size to 1 (check comments in the code).

Troubleshooting "Access Denied" on IMFVirtualCamera::Start method

If you get access denied here, it's probably the same issue as for the native version smourier/VCamSample#1

Here is a summary:

• The COM object that serves as a Virtual Camera Source (here VCamNetSampleSource.comhost.dll) must be accessible by the two Windows 11 services Frame Server & Frame Server Monitor (running as svchost.exe).
• These two services usually run as Local Service & Local System credentials respectively.
• If you compile or build in a directory under your compiling user's root, for example something like C:\Users\<your login>\source\repos\VCamNetSample\VCamNetSampleSource\bin\Debug\net8.0-windows10.0.22621.0 or somewhere restricted in some way, it won't work since these two services will need to access that.

=> So the solution is just to either copy the output directory once built (or downloaded) somewhere where everyone has access and register VCamNetSampleSource.comhost.dll from there, or copy/checkout the whole repo where everyone has access and build and register there.

Tracing

The code output lots of interesting traces. It's quite important in this virtual camera environment because there's not just your process that's involved but at least 4: the VCamNetSample app, the Windows Frame Server, the Windows camera monitor, and the reader app (camera, etc.). They all load the media source COM object in-process.

The solution also contains a small DebuggerAttach project that can be ran to attach to the Windows Frame Server (hosted in svchost.exe). For it to run you must run Visual Studio and DebuggerAttach as administrator. You can also attach to the Frame Server using Visual Studio attach to process once it's been started.

Tracing here doesn't use OutputDebugString because it's 100% old, crappy, truncating text, slow, etc. Instead it uses Event Tracing for Windows ("ETW") in "string-only" mode (the mode where it's very simple and you don't have to register painfull traces records and use complex readers...).

So to read these ETW traces, use WpfTraceSpy you can download here https://github.com/smourier/TraceSpy. Configure an ETW Provider with the GUID set to 964d4572-adb9-4f3a-8170-fcbecec27467