7.15. ioctl VIDIOC_ENUM_FRAMESIZES¶

7.15.1. Name¶

VIDIOC_ENUM_FRAMESIZES - Enumerate frame sizes

7.15.2. Synopsis¶

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

7.15.3. Arguments¶

fd: File descriptor returned by open().
argp: Pointer to struct v4l2_frmsizeenum that contains an index and pixel format and receives a frame width and height.

7.15.4. 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.

注釈

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.

7.15.5. 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.

7.15.6. 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.

7.15.7. 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.