VIDIOC_ENUM_FRAMESIZES — Enumerate frame sizes
int ioctl( | int fd, |
| int request, | |
struct v4l2_frmsizeenum *argp); |
fdFile descriptor returned by open().
requestVIDIOC_ENUM_FRAMESIZES
argpPointer to a struct v4l2_frmsizeenum that contains an index and pixel format and receives a frame width and height.
This ioctl allows applications to enumerate all frame sizes (i. e. width and height in pixels) that the device supports for the given pixel format.
The supported pixel formats can be obtained by using the
VIDIOC_ENUM_FMT function.
The return value and the content of the
v4l2_frmsizeenum.type field depend on the
type of frame sizes the device supports. Here are the semantics of the
function for the different cases:
Discrete: The function
returns success if the given index value (zero-based) is valid. The
application should increase the index by one for each call until
EINVAL is returned. The
v4l2_frmsizeenum.type field is set to
V4L2_FRMSIZE_TYPE_DISCRETE by the driver. Of the
union only the discrete member is
valid.
Step-wise: The function
returns success if the given index value is zero and
EINVAL for any other index value. The
v4l2_frmsizeenum.type field is set to
V4L2_FRMSIZE_TYPE_STEPWISE by the driver. Of the
union only the stepwise member is
valid.
Continuous: This is a
special case of the step-wise type above. The function returns success
if the given index value is zero and EINVAL for
any other index value. The
v4l2_frmsizeenum.type field is set to
V4L2_FRMSIZE_TYPE_CONTINUOUS by the driver. Of
the union only the stepwise member is valid
and the step_width and
step_height values are set to 1.
When the application calls the function with index zero, it
must check the type field to determine the
type of frame size enumeration the device supports. Only for the
V4L2_FRMSIZE_TYPE_DISCRETE type does it make
sense to increase the index value to receive more frame sizes.
Note that the order in which the frame sizes are returned has no special meaning. In particular does it not say anything about potential default format sizes.
Applications can assume that the enumeration data does not change without any interaction from the application itself. This means that the enumeration data is consistent if the application does not perform any other ioctl calls while it runs the frame size enumeration.
In the structs below, IN denotes a value that has to be filled in by the application, OUT denotes values that the driver fills in. The application should zero out all members except for the IN fields.
Table A.30. struct v4l2_frmsize_discrete
| __u32 | width | Width of the frame [pixel]. |
| __u32 | height | Height of the frame [pixel]. |
Table A.31. struct v4l2_frmsize_stepwise
| __u32 | min_width | Minimum frame width [pixel]. |
| __u32 | max_width | Maximum frame width [pixel]. |
| __u32 | step_width | Frame width step size [pixel]. |
| __u32 | min_height | Minimum frame height [pixel]. |
| __u32 | max_height | Maximum frame height [pixel]. |
| __u32 | step_height | Frame height step size [pixel]. |
Table A.32. struct v4l2_frmsizeenum
| __u32 | index | IN: Index of the given frame size in the enumeration. | |
| __u32 | pixel_format | IN: Pixel format for which the frame sizes are enumerated. | |
| __u32 | type | OUT: Frame size type the device supports. | |
| union | OUT: Frame size with the given index. | ||
| struct v4l2_frmsize_discrete | discrete | ||
| struct v4l2_frmsize_stepwise | stepwise | ||
| __u32 | reserved[2] | Reserved space for future use. Must be zeroed by drivers and applications. |
Table A.33. enum v4l2_frmsizetypes
V4L2_FRMSIZE_TYPE_DISCRETE | 1 | Discrete frame size. |
V4L2_FRMSIZE_TYPE_CONTINUOUS | 2 | Continuous frame size. |
V4L2_FRMSIZE_TYPE_STEPWISE | 3 | Step-wise defined frame size. |
On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.