capturing and overlay with a single file descriptor for compatibility
with V4L and earlier versions of V4L2. [#f1]_
+A common application of two file descriptors is the X11
+:ref:`Xv/V4L <xvideo>` interface driver and a V4L2 application.
+While the X server controls video overlay, the application can take
+advantage of memory mapping and DMA.
Querying Capabilities
=====================
:ref:`VIDIOC_OVERLAY` ioctl.
.. [#f1]
- A common application of two file descriptors is the XFree86
- :ref:`Xv/V4L <xvideo>` interface driver and a V4L2 application.
- While the X server controls video overlay, the application can take
- advantage of memory mapping and DMA.
-
In the opinion of the designers of this API, no driver writer taking
the efforts to support simultaneous capturing and overlay will
restrict this ability by requiring a single file descriptor, as in