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. For compressed formats that contain the resolution information encoded inside the stream, when fed to a stateful mem2mem decoder, the fields may be zero to rely on the decoder to detect the right values. For more details see Memory-to-Memory Stateful Video Decoder Interface and format descriptions. For compressed formats on the CAPTURE side of a stateful mem2mem encoder, the fields must be zero, since the coded size is expected to be calculated internally by the encoder itself, based on the OUTPUT side. For more details see Memory-to-Memory Stateful Video Encoder Interface and format descriptions.
__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. If the application sets the flag V4L2_PIX_FMT_FLAG_SET_CSC then the application can set this field for a capture stream to request a specific colorspace for the captured image data. If the driver cannot handle requested conversion, it will return another supported colorspace. The driver indicates that colorspace conversion is supported by setting the flag V4L2_FMT_FLAG_CSC_COLORSPACE in the corresponding struct v4l2_fmtdesc during enumeration. See Image Format Description Flags.
__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. If the application sets the flag V4L2_PIX_FMT_FLAG_SET_CSC then the application can set this field for a capture stream to request a specific Y’CbCr encoding for the captured image data. If the driver cannot handle requested conversion, it will return another supported encoding. This field is ignored for HSV pixelformats. The driver indicates that ycbcr_enc conversion is supported by setting the flag V4L2_FMT_FLAG_CSC_YCBCR_ENC in the corresponding struct v4l2_fmtdesc during enumeration. See Image Format Description Flags.
__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. If the application sets the flag V4L2_PIX_FMT_FLAG_SET_CSC then the application can set this field for a capture stream to request a specific HSV encoding for the captured image data. If the driver cannot handle requested conversion, it will return another supported encoding. This field is ignored for non-HSV pixelformats. The driver indicates that hsv_enc conversion is supported by setting the flag V4L2_FMT_FLAG_CSC_HSV_ENC in the corresponding struct v4l2_fmtdesc during enumeration. See Image Format Description Flags.
}
__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. If the application sets the flag V4L2_PIX_FMT_FLAG_SET_CSC then the application can set this field for a capture stream to request a specific quantization range for the captured image data. If the driver cannot handle requested conversion, it will return another supported quantization. The driver indicates that quantization conversion is supported by setting the flag V4L2_FMT_FLAG_CSC_QUANTIZATION in the corresponding struct v4l2_fmtdesc during enumeration. See Image Format Description Flags.
__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. If the application sets the flag V4L2_PIX_FMT_FLAG_SET_CSC then the application can set this field for a capture stream to request a specific transfer function for the captured image data. If the driver cannot handle requested conversion, it will return another supported transfer function. The driver indicates that xfer_func conversion is supported by setting the flag V4L2_FMT_FLAG_CSC_XFER_FUNC in the corresponding struct v4l2_fmtdesc during enumeration. See Image Format Description Flags.

Format Flags

V4L2_PIX_FMT_FLAG_PREMUL_ALPHA	0x00000001	The color values are premultiplied by the alpha channel value. For example, if a light blue pixel with 50% transparency was described by RGBA values (128, 192, 255, 128), the same pixel described with premultiplied colors would be described by RGBA values (64, 96, 128, 128)
V4L2_PIX_FMT_FLAG_SET_CSC	0x00000002	Set by the application. It is only used for capture and is ignored for output streams. If set, then request the device to do colorspace conversion from the received colorspace to the requested colorspace values. If the colorimetry field (colorspace, xfer_func, ycbcr_enc, hsv_enc or quantization) is set to *_DEFAULT, then that colorimetry setting will remain unchanged from what was received. So in order to change the quantization, only the quantization field shall be set to non default value (V4L2_QUANTIZATION_FULL_RANGE or V4L2_QUANTIZATION_LIM_RANGE) and all other colorimetry fields shall be set to *_DEFAULT. To check which conversions are supported by the hardware for the current pixel format, see Image Format Description Flags.