Implementing video capture

Video capture involves several tasks, including reserving memory, connecting to a capture device, and releasing memory once the capture is finished.


To capture video, you need to:
  • reserve memory for the video frame and metadata buffers
  • connect to the capture device and set up the capture context
  • validate the capture device's properties
  • set the capture parameters
  • start the video capture
  • stop the capture
  • destroy the buffers to release the memory they use
Note the following about video capture:
  • The processes that use capture must be privileged processes.
  • The video capture service does not handle displaying the captured video. For this, you need to use another resource, such a Screen.

Video capture code that you can use for reference is available in "Sample video capture program".


Before it starts video capture, your program needs to:

If your hardware doesn't support dynamic memory allocation and it requires you to use memory in a preallocated location, you will need to use capture_create_buffers() to create your buffers. For more information about this special case, see "Video capture buffers" in this guide.

Video capture tasks

To capture video, you need to perform the following tasks:

Set up context
  1. Video capture requires a video capture context to which you can connect your input device. To create a video capture context, call capture_create_context(). This function returns a pointer to the capture context in the capture_context_t data structure, which you will then pass to your other functions during the video capture session.
Validate capture device properties
  1. Call capture_get_property_p() to get information about the capture device.
  2. Call capture_is_property() to check if the driver supports a property. Call this function once for each property you need to check.
Set the capture parameters
  1. Call capture_set_property_i() for each capture property you need to set, using the CAPTURE_PROPERTY_* constants to set the device, brightness, destination buffers, etc.
  2. Call capture_set_property_p() to hand the pointer to your properties array to the video capture library.
Capture the video frames
  1. Make a final call to capture_set_property_i() with the second argument set to CAPTURE_ENABLE and the third argument set to 1 (one) to instruct the driver to start video capture when capture_update() is called.
  2. Call capture_update() to start the video capture.
  3. Create a loop to call capture_get_frame() to get the video frames from the hardware.
  4. You can use the Screen function screen_post_window() to post the video frame for display in your screen window.
  5. After you have posted a frame, mark the buffer that was used for the frame as available for reuse by calling capture_release_frame().
Stop and clean up
  1. When you want to stop video capture, call capture_set_property_i() with the second argument set to CAPTURE_ENABLE and the third argument set to 0 (zero) to disable video capture.
  2. Call capture_update() to stop video capture.
  3. If you will not restart video capture again immediately (the session is stopped rather than paused), your application must call capture_destroy_context() to destroy all contexts before it releases the capture buffers and exits.
    • The capture_destroy_context() function is not signal handler safe! For recommendations on how to use capture_destroy_context() see the documentation for this function.
    • You can't count on the OS being able to adequately clean up after your application exits, if the application does not destroy all the contexts it created for video capture. Failure to destroy a context before exiting can lead to memory corruption and unpredicatable system behavior.