7.14. ioctl VIDIOC_ENUM_FMT¶

7.14.1. Name¶

VIDIOC_ENUM_FMT - Enumerate image formats

7.14.2. Synopsis¶

VIDIOC_ENUM_FMT¶

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, mbus_code and index fields 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. If applicable, drivers shall return formats in preference order, where preferred formats are returned before (that is, with lower index value) less-preferred formats.

Depending on the V4L2_CAP_IO_MC capability, the mbus_code field is handled differently:

V4L2_CAP_IO_MC is not set (also known as a ‘video-node-centric’ driver)

Applications shall initialize the mbus_code field to zero and drivers shall ignore the value of the field.

Drivers shall enumerate all image formats.

Note

After switching the input or output the list of enumerated image formats may be different.
V4L2_CAP_IO_MC is set (also known as an ‘MC-centric’ driver)

If the mbus_code field is zero, then all image formats shall be enumerated.

If the mbus_code field is initialized to a valid (non-zero) media bus format code, then drivers shall restrict enumeration to only the image formats that can produce (for video output devices) or be produced from (for video capture devices) that media bus code. If the mbus_code is unsupported by the driver, then EINVAL shall be returned.

Regardless of the value of the mbus_code field, the enumerated image formats shall not depend on the active configuration of the video device or device pipeline.

type 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`, `V4L2_BUF_TYPE_META_CAPTURE` and `V4L2_BUF_TYPE_META_OUTPUT`. 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. Attention These codes are not the same as those used in the Windows world.
__u32	`mbus_code`	Media bus code restricting the enumerated formats, set by the application. Only applicable to drivers that advertise the `V4L2_CAP_IO_MC` capability, shall be 0 otherwise.
__u32	`reserved`[3]	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. This flag is valid for stateful codecs only.
`V4L2_FMT_FLAG_ENC_CAP_FRAME_INTERVAL`	0x0010	The hardware encoder supports setting the `CAPTURE` coded frame interval separately from the `OUTPUT` raw frame interval. Setting the `OUTPUT` raw frame interval with VIDIOC_S_PARM also sets the `CAPTURE` coded frame interval to the same value. If this flag is set, then the `CAPTURE` coded frame interval can be set to a different value afterwards. This is typically used for offline encoding where the `OUTPUT` raw frame interval is used as a hint for reserving hardware encoder resources and the `CAPTURE` coded frame interval is the actual frame rate embedded in the encoded video stream. 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 encoders only.
`V4L2_FMT_FLAG_CSC_COLORSPACE`	0x0020	The driver allows the application to try to change the default colorspace. This flag is relevant only for capture devices. The application can ask to configure the colorspace of the capture device when calling the VIDIOC_S_FMT ioctl with V4L2_PIX_FMT_FLAG_SET_CSC set.
`V4L2_FMT_FLAG_CSC_XFER_FUNC`	0x0040	The driver allows the application to try to change the default transfer function. This flag is relevant only for capture devices. The application can ask to configure the transfer function of the capture device when calling the VIDIOC_S_FMT ioctl with V4L2_PIX_FMT_FLAG_SET_CSC set.
`V4L2_FMT_FLAG_CSC_YCBCR_ENC`	0x0080	The driver allows the application to try to change the default Y’CbCr encoding. This flag is relevant only for capture devices. The application can ask to configure the Y’CbCr encoding of the capture device when calling the VIDIOC_S_FMT ioctl with V4L2_PIX_FMT_FLAG_SET_CSC set.
`V4L2_FMT_FLAG_CSC_HSV_ENC`	0x0080	The driver allows the application to try to change the default HSV encoding. This flag is relevant only for capture devices. The application can ask to configure the HSV encoding of the capture device when calling the VIDIOC_S_FMT ioctl with V4L2_PIX_FMT_FLAG_SET_CSC set.
`V4L2_FMT_FLAG_CSC_QUANTIZATION`	0x0100	The driver allows the application to try to change the default quantization. This flag is relevant only for capture devices. The application can ask to configure the quantization of the capture device when calling the VIDIOC_S_FMT ioctl with V4L2_PIX_FMT_FLAG_SET_CSC set.

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.

If V4L2_CAP_IO_MC is set and the specified mbus_code is unsupported, then also return this error code.