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. If applicable, drivers shall return
formats in preference order, where preferred formats are returned before
(that is, with lower index
value) less-preferred formats.
Note
After switching input or output the list of enumerated image formats may be different.
-
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: |
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 | reserved [4] |
Reserved for future extensions. Drivers must set the array to zero. |
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 theindex
is out of bounds.