Certain USB cameras have several hardware buttons on them. Typically a button triggers a video frame capture. Is there a way to intercept USB-camera harware buttons using Media Foundation interfaces? In the docs I found a cryptic attriute: (https://learn.microsoft.com/en-us/windows/win32/medfound/mf-devicestream-takephoto-trigger MF_SOURCE_READER_FIRST_VIDEO_STREAM) but there is no hint at the way it could be used.
In Directshow a source filter for the same camera exposes two pins - one foe video preview stream and another pin for the still image which sends a sample downstream everytime the hardware trigger is clicked. So technically the driver stack seems to be aware of this camera function (which is in fact a USB protocol feature), but I cannot find any documentation on the issue.