7.16. ioctl VIDIOC_ENUM_FRAMEINTERVALS¶

7.16.1. Name¶

VIDIOC_ENUM_FRAMEINTERVALS - Enumerate frame intervals

7.16.2. Synopsis¶

int ioctl(int fd, VIDIOC_ENUM_FRAMEINTERVALS, struct v4l2_frmivalenum *argp)¶

7.16.3. Arguments¶

fd: File descriptor returned by open().
argp: Pointer to struct v4l2_frmivalenum that contains a pixel format and size and receives a frame interval.

7.16.4. Description¶

This ioctl allows applications to enumerate all frame intervals that the device supports for the given pixel format and frame size.

The supported pixel formats and frame sizes can be obtained by using the ioctl VIDIOC_ENUM_FMT and ioctl VIDIOC_ENUM_FRAMESIZES functions.

The return value and the content of the v4l2_frmivalenum.type field depend on the type of frame intervals 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_frmivalenum.type field is set to V4L2_FRMIVAL_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_frmivalenum.type field is set to V4L2_FRMIVAL_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_frmivalenum.type field is set to V4L2_FRMIVAL_TYPE_CONTINUOUS by the driver. Of the union only the stepwise member is valid and the step value is set to 1.

When the application calls the function with index zero, it must check the type field to determine the type of frame interval enumeration the device supports. Only for the V4L2_FRMIVAL_TYPE_DISCRETE type does it make sense to increase the index value to receive more frame intervals.

注釈

The order in which the frame intervals are returned has no special meaning. In particular does it not say anything about potential default frame intervals.

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 interval enumeration.

注釈

Frame intervals and frame rates: The V4L2 API uses frame intervals instead of frame rates. Given the frame interval the frame rate can be computed as follows:

frame_rate = 1 / frame_interval

7.16.5. 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_frmival_stepwise¶

struct v4l2_frmival_stepwise¶
struct `v4l2_fract`	`min`	Minimum frame interval [s].
struct `v4l2_fract`	`max`	Maximum frame interval [s].
struct `v4l2_fract`	`step`	Frame interval step size [s].

v4l2_frmivalenum¶

struct v4l2_frmivalenum¶
__u32	`index`		IN: Index of the given frame interval in the enumeration.
__u32	`pixel_format`		IN: Pixel format for which the frame intervals are enumerated.
__u32	`width`		IN: Frame width for which the frame intervals are enumerated.
__u32	`height`		IN: Frame height for which the frame intervals are enumerated.
__u32	`type`		OUT: Frame interval type the device supports.
union			OUT: Frame interval with the given index.
	struct `v4l2_fract`	`discrete`	Frame interval [s].
	struct `v4l2_frmival_stepwise`	`stepwise`
__u32	`reserved[2]`		Reserved space for future use. Must be zeroed by drivers and applications.

7.16.6. Enums¶

v4l2_frmivaltypes¶

enum v4l2_frmivaltypes¶
`V4L2_FRMIVAL_TYPE_DISCRETE`	1	Discrete frame interval.
`V4L2_FRMIVAL_TYPE_CONTINUOUS`	2	Continuous frame interval.
`V4L2_FRMIVAL_TYPE_STEPWISE`	3	Step-wise defined frame interval.

7.16.7. 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.