7.14. ioctl VIDIOC_ENUM_FMT¶
7.14.1. Name¶
VIDIOC_ENUM_FMT - Enumerate image formats
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 thembus_code
is unsupported by the driver, thenEINVAL
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.
-
v4l2_fmtdesc
¶
__u32 |
|
Number of the format in the enumeration, set by the application.
This is in no way related to the |
__u32 |
|
Type of the data stream, set by the application. Only these types
are valid here: |
__u32 |
|
|
__u8 |
|
Description of the format, a NUL-terminated ASCII string. This information is intended for the user, for example: “YUV 4:2:2”. |
__u32 |
|
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 |
|
Media bus code restricting the enumerated formats, set by the
application. Only applicable to drivers that advertise the
|
__u32 |
|
Reserved for future extensions. Drivers must set the array to zero. |
|
0x0001 |
This is a compressed format. |
|
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. |
|
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
|
|
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 This flag can only be used in combination with the
|
|
0x0010 |
The hardware encoder supports setting the This flag can only be used in combination with the
|
|
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. |
|
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. |
|
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. |
|
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. |
|
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 theindex
is out of bounds.If
V4L2_CAP_IO_MC
is set and the specifiedmbus_code
is unsupported, then also return this error code.