Name

VIDIOC_ENUM_FMT — Enumerate image formats

Synopsis

int ioctl(int fd,
 int request,
 struct v4l2_fmtdesc *argp);
 

Arguments

fd

File descriptor returned by open().

request

VIDIOC_ENUM_FMT

argp

Description

To enumerate image formats applications initialize the type and index field of struct v4l2_fmtdesc and call the VIDIOC_ENUM_FMT ioctl with a pointer to this structure. Drivers fill the rest of the structure or return an EINVAL error code. All formats are enumerable by beginning at index zero and incrementing by one until EINVAL is returned.

Note that after switching input or output the list of enumerated image formats may be different.

Table A.24. struct v4l2_fmtdesc

__u32indexNumber of the format in the enumeration, set by the application. This is in no way related to the pixelformat field.
__u32typeType of the data stream, set by the application. Only these types are valid here: V4L2_BUF_TYPE_VIDEO_CAPTURE, V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE, V4L2_BUF_TYPE_VIDEO_OUTPUT, V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE and V4L2_BUF_TYPE_VIDEO_OVERLAY. See Table 3.3, “enum v4l2_buf_type”.
__u32flagsSee Table A.25, “Image Format Description Flags”
__u8description[32]Description of the format, a NUL-terminated ASCII string. This information is intended for the user, for example: "YUV 4:2:2".
__u32pixelformatThe image format identifier. This is a four character code as computed by the v4l2_fourcc() macro:

#define v4l2_fourcc(a,b,c,d) (((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24))

Several image formats are already defined by this specification in Chapter 2, Image Formats. Note these codes are not the same as those used in the Windows world.

__u32reserved[4]Reserved for future extensions. Drivers must set the array to zero.

Table A.25. Image Format Description Flags

V4L2_FMT_FLAG_COMPRESSED0x0001This is a compressed format.
V4L2_FMT_FLAG_EMULATED0x0002This format is not native to the device but emulated through software (usually libv4l2), where possible try to use a native format instead for better performance.

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.

EINVAL

The struct v4l2_fmtdesc type is not supported or the index is out of bounds.