Video4Linux

Video4Linux refers to the Linux kernel API and accompanying device drivers that provide standardized access to video capture and output devices. It is the primary framework used on Linux to interface with cameras, TV tuners, capture cards, and similar hardware, exposing devices as file nodes such as /dev/video0.

The project began with the original Video4Linux (V4L) in the late 1990s and evolved into Video4Linux2 (V4L2), which is the current, widely supported interface in modern kernels. V4L2 expands and refines the API to support a broader range of devices, streaming I/O, new pixel formats, and richer control over video capture. Compatibility layers exist to help older software continue to operate with the newer interface.

Software interacts with video4linux devices primarily through the V4L2 API via ioctl system calls. Typical operations include probing device capabilities, configuring image formats and frame sizes, and managing buffers for video data. Data transfer can be done using memory-mapped buffers or user pointer methods, with multiple I/O methods supported depending on the device. The API also provides controls for device-specific settings such as brightness, contrast, and focus.

In userspace, libraries and tools such as libv4l2 and v4l-utils help detect, query, and configure devices. Many multimedia frameworks and applications—such as FFmpeg, GStreamer, OpenCV, and VLC—rely on V4L2 to access cameras and capture video on Linux. Because V4L2 is part of the Linux kernel, it serves as the standard foundation for a broad ecosystem of hardware and software in Linux-based video capture.