Issue Activating Virtual Camera via Media Foundation Win32 API (HRESULT 0x80070057 - Invalid Parameter) after Windows Update Hello, I am trying to use a virtual camera with Windows Media Foundation API on Windows 11. The camera is correctly detected by

Question

Hello,

I am trying to use a virtual camera with Windows Media Foundation API on Windows 11. The camera is correctly detected by MFEnumDeviceSources, but when I try to call ActivateObject(IID_IMFMediaSource, …) on virtual camera, I get the following error:

Failed to activate device Virtual Webcam, error: -2147024809 (0x80070057) - Invalid parameter.

The camera was working fine until the update two months ago.

Problem Details:

• Virtual camera is correctly detected by MFEnumDeviceSources and returns a valid symbolic link.

ActivateObject works on other cameras (such as my Logitech physical USB webcam).

Virtual camera works fine in other applications (e.g., Teams, Zoom).

The same configuration worked on an earlier version of Windows (before a recent update).

Questions:

Why can Virtual Camera not be activated with ActivateObject() while it works in other applications?

How can I debug this activation issue more deeply? Is there a way to check which validations are failing in ActivateObject()?

Could a Windows Media Foundation update be causing this issue?

How did a Windows update cause virtual cameras to no longer be detected using the Win32 API?

Thank you in advance for any help or suggestions!