Как получить информацию об устройствах захвата видео?

OpenCV-х VideoCapture :: get (int propId) может получить вам следующую информацию

CV_CAP_PROP_POS_MSEC      Current position of the video file in milliseconds or video capture timestamp.
CV_CAP_PROP_POS_FRAMES    0-based index of the frame to be decoded/captured next.
CV_CAP_PROP_POS_AVI_RATIO Relative position of the video file: 0 - start of the film, 1 - end of the film.
CV_CAP_PROP_FRAME_WIDTH   Width of the frames in the video stream.
CV_CAP_PROP_FRAME_HEIGHT  Height of the frames in the video stream.
CV_CAP_PROP_FPS           Frame rate.
CV_CAP_PROP_FOURCC        4-character code of codec.
CV_CAP_PROP_FRAME_COUNT   Number of frames in the video file.
CV_CAP_PROP_FORMAT        Format of the Mat objects returned by retrieve() .
CV_CAP_PROP_MODE          Backend-specific value indicating the current capture mode.
CV_CAP_PROP_BRIGHTNESS    Brightness of the image (only for cameras).
CV_CAP_PROP_CONTRAST      Contrast of the image (only for cameras).
CV_CAP_PROP_SATURATION    Saturation of the image (only for cameras).
CV_CAP_PROP_HUE           Hue of the image (only for cameras).
CV_CAP_PROP_GAIN          Gain of the image (only for cameras).
CV_CAP_PROP_EXPOSURE      Exposure (only for cameras).
CV_CAP_PROP_CONVERT_RGB   Boolean flags indicating whether images should be converted to RGB.
CV_CAP_PROP_WHITE_BALANCE Currently not supported
CV_CAP_PROP_RECTIFICATION Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently)

Например:

VideoCapture cap(0); // open the default camera
if(!cap.isOpened())  // check it exists
return -1;
double fps = cap.get(CV_CAP_PROP_FPS);