7.4. ioctl VIDIOC_CROPCAP¶
VIDIOC_CROPCAP - Information about the video cropping and scaling abilities
ioctl(int fd, VIDIOC_CROPCAP, struct v4l2_cropcap *argp)¶
- File descriptor returned by open().
- Pointer to struct
Applications use this function to query the cropping limits, the pixel
aspect of images and to calculate scale factors. They set the
field of a v4l2_cropcap structure to the respective buffer (stream)
type and call the ioctl VIDIOC_CROPCAP ioctl with a pointer to this
structure. Drivers fill the rest of the structure. The results are
constant except when switching the video standard. Remember this switch
can occur implicit when switching the video input or output.
This ioctl must be implemented for video capture or output devices that support cropping and/or scaling and/or have non-square pixels, and for overlay devices.
||Type of the data stream, set by the application. Only these types
are valid here:
||Defines the window within capturing or output is possible, this may exclude for example the horizontal and vertical blanking areas. The cropping rectangle cannot exceed these limits. Width and height are defined in pixels, the driver writer is free to choose origin and units of the coordinate system in the analog domain.|
||Default cropping rectangle, it shall cover the “whole picture”.
Assuming pixel aspect 1/1 this could be for example a 640 × 480
rectangle for NTSC, a 768 × 576 rectangle for PAL and SECAM
centered over the active picture area. The same co-ordinate system
This is the pixel aspect (y / x) when no scaling is applied, the ratio of the actual sampling frequency and the frequency required to get square pixels.
When cropping coordinates refer to square pixels, the driver sets
Unfortunately in the case of multiplanar buffer types
this API was messed up with regards to how the
should be filled in. Some drivers only accepted the
_MPLANE buffer type while
other drivers only accepted a non-multiplanar buffer type (i.e. without the
_MPLANE at the end).
Starting with kernel 4.13 both variations are allowed.
||Horizontal offset of the top, left corner of the rectangle, in pixels.|
||Vertical offset of the top, left corner of the rectangle, in pixels.|
||Width of the rectangle, in pixels.|
||Height of the rectangle, in pixels.|
7.4.5. 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.
- The struct
- Cropping is not supported for this input or output.