OBS Virtual Camera output on Windows / DirectShow only delivers one initial frame

Operating System Info

Windows 10

Other OS

No response

OBS Studio Version

29.0.0

OBS Studio Version (Other)

No response

OBS Studio Log URL

https://obsproject.com/logs/cqdLGkkHCiz62seI

OBS Studio Crash Log URL

No response

Expected Behavior

OBS Virtual Camera should work with DirectShow clients

Current Behavior

After upgrading to OBS Studio 29 from an older version (don't remember which one exactly but it was probably older than a year!), I noticed that the OBS Virtual Camera no longer works properly with software that is built on Qt 5's camera capturing code. While Qt 6 uses Media Foundation for camera capturing on Windows, Qt 5 still uses DirectShow. When using the OBS Virtual Camera this way, I get a single frozen frame and no more frames are delivered. It's not just Qt's sample code that is affected, but real applications built on Qt5 as well, but the sample code is probably the easiest to verify the problem (as OBS is also built on Qt).

Steps to Reproduce

1. Open the declarative-camera example in QtCreator (note: Qt6 does not seem to ship with this example anymore, but it is part of Qt5 installations) (edit: The multimedia module needs to be installed for the Qt6 camera examples to be present. They do not support the OBS Virtual Camera, though.)
2. Run and configure it to use the OBS Virtual Camera as input
3. Observe that the received frame is frozen.

Anything else we should know?

No response

Reproduce the issue with the Qt 5 declarative-camera example configured for OBS Virtual Camera on Windows, using the provided OBS log for context. Trace the OBS Virtual Camera DirectShow path and verify that clients receive continuous frames rather than one frozen initial frame.