The OSD function is accessible through the same character special file
as the :ref:`Video Output <capture>` function.
-.. note:: The default function of such a ``/dev/video`` device is video
+.. note::
+
+ The default function of such a ``/dev/video`` device is video
capturing or output. The OSD function is only available after calling
the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
Devices supporting the *Video Output Overlay* interface set the
``V4L2_CAP_VIDEO_OUTPUT_OVERLAY`` flag in the ``capabilities`` field of
-struct :ref:`v4l2_capability <v4l2-capability>` returned by the
+struct :c:type:`v4l2_capability` returned by the
:ref:`VIDIOC_QUERYCAP` ioctl.
applications can find the corresponding framebuffer device by calling
the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` ioctl. It returns, amongst
other information, the physical address of the framebuffer in the
-``base`` field of struct :ref:`v4l2_framebuffer <v4l2-framebuffer>`.
+``base`` field of struct :c:type:`v4l2_framebuffer`.
The framebuffer device ioctl ``FBIOGET_FSCREENINFO`` returns the same
address in the ``smem_start`` field of struct
-:c:type:`struct fb_fix_screeninfo`. The ``FBIOGET_FSCREENINFO``
-ioctl and struct :c:type:`struct fb_fix_screeninfo` are defined in
+struct :c:type:`fb_fix_screeninfo`. The ``FBIOGET_FSCREENINFO``
+ioctl and struct :c:type:`fb_fix_screeninfo` are defined in
the ``linux/fb.h`` header file.
The width and height of the framebuffer depends on the current video
(or none) of the clipping/blending methods defined for the
:ref:`Video Overlay <overlay>` interface.
-A struct :ref:`v4l2_window <v4l2-window>` defines the size of the
+A struct :c:type:`v4l2_window` defines the size of the
source rectangle, its position in the framebuffer and the
clipping/blending method to be used for the overlay. To get the current
parameters applications set the ``type`` field of a struct
-:ref:`v4l2_format <v4l2-format>` to
+:c:type:`v4l2_format` to
``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` and call the
:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl. The driver fills the
-:ref:`struct v4l2_window <v4l2-window>` substructure named ``win``. It is not
+struct :c:type:`v4l2_window` substructure named ``win``. It is not
possible to retrieve a previously programmed clipping list or bitmap.
To program the source rectangle applications set the ``type`` field of a
-struct :ref:`v4l2_format <v4l2-format>` to
+struct :c:type:`v4l2_format` to
``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``, initialize the ``win``
substructure and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
The driver adjusts the parameters against hardware limits and returns
about driver capabilities without actually changing driver state. Unlike
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` this also works after the overlay has been enabled.
-A struct :ref:`v4l2_crop <v4l2-crop>` defines the size and position
+A struct :c:type:`v4l2_crop` defines the size and position
of the target rectangle. The scaling factor of the overlay is implied by
-the width and height given in struct :ref:`v4l2_window <v4l2-window>`
-and struct :ref:`v4l2_crop <v4l2-crop>`. The cropping API applies to
+the width and height given in struct :c:type:`v4l2_window`
+and struct :c:type:`v4l2_crop`. The cropping API applies to
*Video Output* and *Video Output Overlay* devices in the same way as to
*Video Capture* and *Video Overlay* devices, merely reversing the
direction of the data flow. For more information see :ref:`crop`.