VIDIOC_CROPCAP — Information about the video cropping and scaling abilities


int ioctl(int fd,
 int request,
 struct v4l2_cropcap *argp);



File descriptor returned by open().





Applications 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.

Do not use the multiplanar buffer types. Use V4L2_BUF_TYPE_VIDEO_CAPTURE instead of V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE and use V4L2_BUF_TYPE_VIDEO_OUTPUT instead of V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE.

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.

Table A.2. struct v4l2_cropcap

__u32typeType of the data stream, set by the application. Only these types are valid here: V4L2_BUF_TYPE_VIDEO_CAPTURE, V4L2_BUF_TYPE_VIDEO_OUTPUT and V4L2_BUF_TYPE_VIDEO_OVERLAY. See Table 3.3, “enum v4l2_buf_type”.
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.
struct v4l2_fractpixelaspect

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 pixelaspect to 1/1. Other common values are 54/59 for PAL and SECAM, 11/10 for NTSC sampled according to [[ITU BT.601]].

Table A.3. struct v4l2_rect

__s32leftHorizontal offset of the top, left corner of the rectangle, in pixels.
__s32topVertical offset of the top, left corner of the rectangle, in pixels.
__u32widthWidth of the rectangle, in pixels.
__u32heightHeight of the rectangle, in pixels.

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 v4l2_cropcap type is invalid.