7.33. ioctl VIDIOC_G_EXT_PIX_FMT, VIDIOC_S_EXT_PIX_FMT, VIDIOC_TRY_EXT_PIX_FMT¶

7.33.1. Name¶

VIDIOC_G_EXT_PIX_FMT - VIDIOC_S_EXT_PIX_FMT - VIDIOC_TRY_EXT_PIX_FMT - Get or set the data format, try a format

7.33.2. Synopsis¶

int ioctl(int fd, VIDIOC_G_EXT_PIX_FMT, struct v4l2_ext_pix_format *argp)¶

int ioctl(int fd, VIDIOC_S_EXT_PIX_FMT, struct v4l2_ext_pix_format *argp)¶

int ioctl(int fd, VIDIOC_TRY_EXT_PIX_FMT, struct v4l2_ext_pix_format *argp)¶

7.33.3. Arguments¶

fd: File descriptor returned by open().
argp: Pointer to struct v4l2_ext_pix_format.

7.33.4. Description¶

These ioctls are used to negotiate the format of data (typically image format) exchanged between driver and application.

To query the current parameters applications set the type field of a struct v4l2_ext_pix_format to V4L2_BUF_TYPE_VIDEO_CAPTURE or V4L2_BUF_TYPE_VIDEO_OUTPUT, all the other types are invalid in this API, and multiplanar is supported through modifiers.

When the application calls the VIDIOC_G_EXT_PIX_FMT ioctl with a pointer to this structure the driver fills the other members. When the requested buffer type is not supported drivers return an EINVAL error code.

To change the current format parameters applications initialize all the fields in the struct. For details see the documentation of the various devices types in Interfaces. Good practice is to query the current parameters first, and to modify only those parameters not suitable for the application. When the application calls the VIDIOC_S_EXT_PIX_FMT ioctl with a pointer to a struct v4l2_ext_pix_format structure the driver checks and adjusts the parameters against hardware abilities. Drivers should not return an error code unless the type field is invalid, this is a mechanism to fathom device capabilities and to approach parameters acceptable for both the application and driver. On success the driver may program the hardware, allocate resources and generally prepare for data exchange. Finally the VIDIOC_S_EXT_PIX_FMT ioctl returns the current format parameters as VIDIOC_G_EXT_PIX_FMT does. Very simple, inflexible devices may even ignore all input and always return the default parameters. However all V4L2 devices exchanging data with the application must implement the VIDIOC_G_EXT_PIX_FMT and VIDIOC_S_EXT_PIX_FMT ioctl. When the requested buffer type is not supported drivers return an EINVAL error code on a VIDIOC_S_EXT_PIX_FMT attempt. When I/O is already in progress or the resource is not available for other reasons drivers return the EBUSY error code.

The VIDIOC_TRY_EXT_PIX_FMT ioctl is equivalent to VIDIOC_S_EXT_PIX_FMT with one exception: it does not change driver state. It can also be called at any time, never returning EBUSY. This function is provided to negotiate parameters, to learn about hardware limitations, without disabling I/O or possibly time consuming hardware preparations. Although strongly recommended drivers are not required to implement this ioctl.

The format as returned by VIDIOC_TRY_EXT_PIX_FMT must be identical to what VIDIOC_S_EXT_PIX_FMT returns for the same input or output.

struct v4l2_plane_ext_pix_format¶: additional, per-plane format definition

Definition

struct v4l2_plane_ext_pix_format {
  __u32 sizeimage;
  __u32 bytesperline;
  __u32 reserved;
};

Members

sizeimage: maximum size in bytes required for data, for which this plane will be used. Should be set to zero for unused planes.
bytesperline: distance in bytes between the leftmost pixels in two adjacent lines
reserved: extra space reserved for future fields, must be set to 0

struct v4l2_ext_pix_format¶: extended single/multiplanar format definition

Definition

struct v4l2_ext_pix_format {
  __u32 type;
  __u32 width;
  __u32 height;
  __u32 field;
  __u64 modifier;
  __u32 pixelformat;
  __u32 colorspace;
  struct v4l2_plane_ext_pix_format plane_fmt[VIDEO_MAX_PLANES];
  union {
    __u32 ycbcr_enc;
    __u32 hsv_enc;
  };
  __u32 quantization;
  __u32 xfer_func;
  __u32 reserved[9];
};

Members

type: type of the data stream; V4L2_BUF_TYPE_VIDEO_CAPTURE or V4L2_BUF_TYPE_VIDEO_OUTPUT
width: image width in pixels
height: image height in pixels
field: enum v4l2_field; field order (for interlaced video)
modifier: modifier applied to the format (used for tiled formats and other kind of HW-specific formats, like compressed formats)
pixelformat: little endian four character code (fourcc)
colorspace: enum v4l2_colorspace; supplemental to pixelformat
plane_fmt: per-plane information
{unnamed_union}: anonymous
ycbcr_enc: enum v4l2_ycbcr_encoding, Y’CbCr encoding
hsv_enc: enum v4l2_hsv_encoding, HSV encoding
quantization: enum v4l2_quantization, colorspace quantization
xfer_func: enum v4l2_xfer_func, colorspace transfer function
reserved: extra space reserved for future fields, must be set to 0

7.33.5. 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_ext_pix_format type field is invalid or the requested buffer type not supported.
EBUSY: The device is busy and cannot change the format. This could be because or the device is streaming or buffers are allocated or queued to the driver. Relevant for VIDIOC_S_EXT_PIX_FMT only.