2.1. Single-planar format structure

v4l2_pix_format
struct v4l2_pix_format
__u32 width Image width in pixels.
__u32 height Image height in pixels. If field is one of V4L2_FIELD_TOP, V4L2_FIELD_BOTTOM or V4L2_FIELD_ALTERNATE then height refers to the number of lines in the field, otherwise it refers to the number of lines in the frame (which is twice the field height for interlaced formats).
Applications set these fields to request an image size, drivers return the closest possible values. In case of planar formats the width and height applies to the largest plane. To avoid ambiguities drivers must return values rounded up to a multiple of the scale factor of any smaller planes. For example when the image format is YUV 4:2:0, width and height must be multiples of two.
__u32 pixelformat The pixel format or type of compression, set by the application. This is a little endian four character code. V4L2 defines standard RGB formats in RGB Formats, YUV formats in YUV Formats, and reserved codes in Reserved Image Formats
__u32 field Field order, from enum v4l2_field. Video images are typically interlaced. Applications can request to capture or output only the top or bottom field, or both fields interlaced or sequentially stored in one buffer or alternating in separate buffers. Drivers return the actual field order selected. For more details on fields see Field Order.
__u32 bytesperline Distance in bytes between the leftmost pixels in two adjacent lines.

Both applications and drivers can set this field to request padding bytes at the end of each line. Drivers however may ignore the value requested by the application, returning width times bytes per pixel or a larger value required by the hardware. That implies applications can just set this field to zero to get a reasonable default.

Video hardware may access padding bytes, therefore they must reside in accessible memory. Consider cases where padding bytes after the last line of an image cross a system page boundary. Input devices may write padding bytes, the value is undefined. Output devices ignore the contents of padding bytes.

When the image format is planar the bytesperline value applies to the first plane and is divided by the same factor as the width field for the other planes. For example the Cb and Cr planes of a YUV 4:2:0 image have half as many padding bytes following each line as the Y plane. To avoid ambiguities drivers must return a bytesperline value rounded up to a multiple of the scale factor.

For compressed formats the bytesperline value makes no sense. Applications and drivers must set this to 0 in that case.

__u32 sizeimage

Size in bytes of the buffer to hold a complete image, set by the driver. Usually this is bytesperline times height. When the image consists of variable length compressed data this is the number of bytes required by the codec to support the worst-case compression scenario.

The driver will set the value for uncompressed images.

Clients are allowed to set the sizeimage field for variable length compressed data flagged with V4L2_FMT_FLAG_COMPRESSED at ioctl VIDIOC_ENUM_FMT, but the driver may ignore it and set the value itself, or it may modify the provided value based on alignment requirements or minimum/maximum size requirements. If the client wants to leave this to the driver, then it should set sizeimage to 0.

__u32 colorspace Image colorspace, from enum v4l2_colorspace. This information supplements the pixelformat and must be set by the driver for capture streams and by the application for output streams, see Colorspaces.
__u32 priv

This field indicates whether the remaining fields of the struct v4l2_pix_format, also called the extended fields, are valid. When set to V4L2_PIX_FMT_PRIV_MAGIC, it indicates that the extended fields have been correctly initialized. When set to any other value it indicates that the extended fields contain undefined values.

Applications that wish to use the pixel format extended fields must first ensure that the feature is supported by querying the device for the V4L2_CAP_EXT_PIX_FORMAT capability. If the capability isn’t set the pixel format extended fields are not supported and using the extended fields will lead to undefined results.

To use the extended fields, applications must set the priv field to V4L2_PIX_FMT_PRIV_MAGIC, initialize all the extended fields and zero the unused bytes of the struct v4l2_format raw_data field.

When the priv field isn’t set to V4L2_PIX_FMT_PRIV_MAGIC drivers must act as if all the extended fields were set to zero. On return drivers must set the priv field to V4L2_PIX_FMT_PRIV_MAGIC and all the extended fields to applicable values.

__u32 flags Flags set by the application or driver, see Format Flags.
union { (anonymous)  
__u32 ycbcr_enc Y’CbCr encoding, from enum v4l2_ycbcr_encoding. This information supplements the colorspace and must be set by the driver for capture streams and by the application for output streams, see Colorspaces.
__u32 hsv_enc HSV encoding, from enum v4l2_hsv_encoding. This information supplements the colorspace and must be set by the driver for capture streams and by the application for output streams, see Colorspaces.
}    
__u32 quantization Quantization range, from enum v4l2_quantization. This information supplements the colorspace and must be set by the driver for capture streams and by the application for output streams, see Colorspaces.
__u32 xfer_func Transfer function, from enum v4l2_xfer_func. This information supplements the colorspace and must be set by the driver for capture streams and by the application for output streams, see Colorspaces.