7.14. ioctl VIDIOC_ENUM_FMT¶

7.14.1. Name¶

VIDIOC_ENUM_FMT - Enumerate image formats

7.14.2. Synopsis¶

int ioctl(int fd, VIDIOC_ENUM_FMT, struct v4l2_fmtdesc *argp)¶

7.14.3. Arguments¶

fd: File descriptor returned by open().
argp: Pointer to struct v4l2_fmtdesc.

7.14.4. Description¶

To enumerate image formats applications initialize the type and index field of struct v4l2_fmtdesc and call the ioctl 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.

注釈

After switching input or output the list of enumerated image formats may be different.

v4l2_fmtdesc¶

struct v4l2_fmtdesc¶
__u32	`index`	Number of the format in the enumeration, set by the application. This is in no way related to the `pixelformat` field.
__u32	`type`	Type 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`, `V4L2_BUF_TYPE_VIDEO_OVERLAY`, `V4L2_BUF_TYPE_SDR_CAPTURE`, `V4L2_BUF_TYPE_SDR_OUTPUT` and `V4L2_BUF_TYPE_META_CAPTURE`. See `v4l2_buf_type`.
__u32	`flags`	See Image Format Description Flags
__u8	`description`[32]	Description of the format, a NUL-terminated ASCII string. This information is intended for the user, for example: "YUV 4:2:2".
__u32	`pixelformat`	The 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 Image Formats. 注意 These codes are not the same as those used in the Windows world.
__u32	`reserved`[4]	Reserved for future extensions. Drivers must set the array to zero.

Image Format Description Flags¶
`V4L2_FMT_FLAG_COMPRESSED`	0x0001	This is a compressed format.
`V4L2_FMT_FLAG_EMULATED`	0x0002	This 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.
`V4L2_FMT_FLAG_CONTINUOUS_BYTESTREAM`	0x0004	The hardware decoder for this compressed bytestream format (aka coded format) is capable of parsing a continuous bytestream. Applications do not need to parse the bytestream themselves to find the boundaries between frames/fields. This flag can only be used in combination with the `V4L2_FMT_FLAG_COMPRESSED` flag, since this applies to compressed formats only. This flag is valid for stateful decoders only.
`V4L2_FMT_FLAG_DYN_RESOLUTION`	0x0008	Dynamic resolution switching is supported by the device for this compressed bytestream format (aka coded format). It will notify the user via the event `V4L2_EVENT_SOURCE_CHANGE` when changes in the video parameters are detected. This flag can only be used in combination with the `V4L2_FMT_FLAG_COMPRESSED` flag, since this applies to compressed formats only. It is also only applies to stateful codecs.

7.14.5. 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.