Table of Contents
The V4L2 API was primarily designed for devices exchanging
image data with applications. The
v4l2_pix_format structure defines the format
and layout of an image in memory. Image formats are negotiated with
the VIDIOC_S_FMT ioctl. (The explanations here focus on video
capturing and output, for overlay frame buffer formats see also
VIDIOC_G_FBUF.)
Table 2.1. struct v4l2_pix_format
| __u32 | width | Image width in pixels. |
| __u32 | height | Image height in pixels. |
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 Table 2.4, “Packed RGB Image Formats”, YUV formats in Section 2.5, “YUV Formats”, and reserved codes in Table 2.8, “Reserved Image Formats” |
| enum v4l2_field | 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 details see Section 3.6, “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 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
| ||
| __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 maximum number of bytes required to
hold an image. |
| enum v4l2_colorspace | colorspace | This information supplements the
pixelformat and must be set by the driver,
see Section 2.2, “Colorspaces”. |
| __u32 | priv | Reserved for custom (driver defined) additional information about formats. When not used drivers and applications must set this field to zero. |