8.15. ioctl VIDIOC_ENUM_FRAMESIZES

8.15.1. Name

VIDIOC_ENUM_FRAMESIZES - Enumerate frame sizes

8.15.2. Synopsis

int ioctl(int fd, VIDIOC_ENUM_FRAMESIZES, struct v4l2_frmsizeenum *argp)

8.15.3. Arguments

fd

File descriptor returned by open().

argp

Pointer to a struct v4l2_frmsizeenum that contains an index and pixel format and receives a frame width and height.

8.15.4. Description

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 ioctl 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

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.

8.15.5. Structs

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.

v4l2_frmsize_discrete

struct v4l2_frmsize_discrete

__u32	width	Width of the frame [pixel].
__u32	height	Height of the frame [pixel].

v4l2_frmsize_stepwise

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].

v4l2_frmsizeenum

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.

8.15.6. Enums

v4l2_frmsizetypes

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.

8.15.7. Return Value

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.