The driver will fill in the rest of the fields. Buffers should be dequeued, refilled and requeued again to keep the data flowing continuously. The caller should be sure there is a buffer in the queue first. Typically, preview is accomplished by writing data into a frame buffer. It could also be the primary graphics surface.
Some devices apply the video overlay to the output of the graphics card.
In this case the frame buffer is not modified by the video device, and the frame buffer address and format are not needed by the driver. They work as described in the capture spec . For example, a control panel application would do this. Fill in the output number in the structure with the video output associated with the modulator, then pass the structure to the ioctl to have the data filled in. Audio A video output may have an audio output too.