7.14. ioctl VIDIOC_ENUM_FMT¶
VIDIOC_ENUM_FMT - Enumerate image formats
To enumerate image formats applications initialize the
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
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
mbus_code field is handled differently:
V4L2_CAP_IO_MCis not set (also known as a ‘video-node-centric’ driver)
Applications shall initialize the
mbus_codefield to zero and drivers shall ignore the value of the field.
Drivers shall enumerate all image formats.
After switching the input or output the list of enumerated image formats may be different.
V4L2_CAP_IO_MCis set (also known as an ‘MC-centric’ driver)
mbus_codefield is zero, then all image formats shall be enumerated.
mbus_codefield 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_codeis unsupported by the driver, then
EINVALshall be returned.
Regardless of the value of the
mbus_codefield, the enumerated image formats shall not depend on the active configuration of the video device or device pipeline.
||Number of the format in the enumeration, set by the application.
This is in no way related to the
||Type of the data stream, set by the application. Only these types
are valid here:
||See Image Format Description Flags|
||Description of the format, a NUL-terminated ASCII string. This information is intended for the user, for example: “YUV 4:2:2”.|
||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.
These codes are not the same as those used in the Windows world.
||Media bus code restricting the enumerated formats, set by the
application. Only applicable to drivers that advertise the
||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
||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
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.
typeis not supported or the
indexis out of bounds.
V4L2_CAP_IO_MCis set and the specified
mbus_codeis unsupported, then also return this error code.