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:

1. 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.

2. 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. When the index is ORed with V4L2_FMTDESC_FLAG_ENUM_ALL the driver clears the flag and enumerates all the possible formats, ignoring any limitations from the current configuration. Drivers which do not support this flag always return an EINVAL error code without clearing this flag. Formats enumerated when using V4L2_FMTDESC_FLAG_ENUM_ALL flag shouldn’t be used when calling VIDIOC_ENUM_FRAMESIZES() or VIDIOC_ENUM_FRAMEINTERVALS(). V4L2_FMTDESC_FLAG_ENUM_ALL should only be used by drivers that can return different format list depending on this flag.
__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.
V4L2_FMT_FLAG_META_LINE_BASED	0x0200	The metadata format is line-based. In this case the width, height and bytesperline fields of v4l2_meta_format are valid. The buffer consists of height lines, each having width Data Units of data and the offset (in bytes) between the beginning of each two consecutive lines is bytesperline.
V4L2_FMTDESC_FLAG_ENUM_ALL	0x80000000	When the applications ORs index with V4L2_FMTDESC_FLAG_ENUM_ALL flag the driver enumerates all the possible pixel formats without taking care of any already set configuration. Drivers which do not support this flag, always return EINVAL without clearing this flag.

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.