V4L2PIXFMT

V4L2_PIX_FMT, commonly referred to in code as V4L2PIX_FMT, denotes the set of pixel format identifiers used by the Video4Linux2 (V4L2) API to describe how image data is laid out in memory. Each format is encoded as a FourCC code, a 32-bit integer created by the v4l2_fourcc macro from four ASCII characters. These codes let applications and drivers agree on how video frames are stored and transferred between devices and software.

The format constants are defined in the V4L2 headers (notably videodev2.h) and are used throughout the API to configure buffers, negotiate formats, and stream video. Examples include V4L2_PIX_FMT_YUYV, V4L2_PIX_FMT_NV12, V4L2_PIX_FMT_YV12, and various RGB variants such as V4L2_PIX_FMT_RGB24 or V4L2_PIX_FMT_BGR24. Formats may be packed (single plane) or multi-planar (separate planes for Y, U, and V components). Proper handling of these formats is essential for correct color representation and memory layout.

Format negotiation in user-space typically involves querying capabilities with VIDIOC_QUERYCAP, enumerating supported formats via VIDIOC_ENUM_FMT, and selecting a format with VIDIOC_S_FMT or trying a format with VIDIOC_TRY_FMT. For frame dimensions and frame intervals, applications use VIDIOC_ENUM_FRAMESIZES and VIDIOC_ENUM_FRAMEINTERVALS.

In summary, V4L2_PIX_FMT provides a compact, standardized way to describe how video data is organized in V4L2-enabled devices, enabling interoperable buffer handling, capture, and display across Linux multimedia software.