ioctl VIDIOC_CROPCAP
&manvol;
VIDIOC_CROPCAPInformation about the video cropping and scaling abilitiesint ioctlint fdint requeststruct v4l2_cropcap
*argpArgumentsfd&fd;requestVIDIOC_CROPCAPargpDescriptionApplications use this function to query the cropping
limits, the pixel aspect of images and to calculate scale factors.
They set the type field of a v4l2_cropcap
structure to the respective buffer (stream) type and call the
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.
struct v4l2_cropcap
&cs-str;
&v4l2-buf-type;typeType of the data stream, set by the application.
Only these types are valid here:
V4L2_BUF_TYPE_VIDEO_CAPTURE,
V4L2_BUF_TYPE_VIDEO_OUTPUT,
V4L2_BUF_TYPE_VIDEO_OVERLAY, and custom (driver
defined) types with code V4L2_BUF_TYPE_PRIVATE
and higher.struct v4l2_rectboundsDefines 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.struct v4l2_rectdefrectDefault 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 as for
bounds is used.&v4l2-fract;pixelaspectThis 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 pixelaspect to 1/1. Other
common values are 54/59 for PAL and SECAM, 11/10 for NTSC sampled
according to [].
struct v4l2_rect
&cs-str;
__s32leftHorizontal offset of the top, left corner of the
rectangle, in pixels.__s32topVertical offset of the top, left corner of the
rectangle, in pixels.__s32widthWidth of the rectangle, in pixels.__s32heightHeight of the rectangle, in pixels. Width
and height cannot be negative, the fields are signed for
hysterical reasons.
&return-value;
EINVALThe &v4l2-cropcap; type is
invalid or the ioctl is not supported. This is not permitted for
video capture, output and overlay devices, which must support
VIDIOC_CROPCAP.