videoio

Video I/O, or video input/output, refers to the set of software interfaces and hardware mechanisms that enable the capture, processing, encoding, decoding, and output of video data. It covers sources such as cameras and capture cards, video files, and network streams, as well as destinations like display devices and video writers. Key concerns include frame rate, resolution, color space, encoding codecs, container formats, buffering, synchronization, and latency.

In software libraries, videoio modules provide an API to open a capture source or a video file, read frames in real time or offline, and write frames to a file or stream. They typically expose operations to query and set properties (frame width, height, fps, codec), control the stream (start, stop), and handle end-of-stream. They rely on backend drivers or frameworks for platform-specific support.

OpenCV and similar toolkits commonly implement a videoio module to unify access to diverse backends. In OpenCV, the videoio component provides video capture and writing capabilities, with top-level interfaces such as VideoCapture and VideoWriter. Backends include V4L2 on Linux, DirectShow or Media Foundation on Windows, AVFoundation on macOS, and other plugins like GStreamer. The module abstracts backend differences, enabling cross-platform code that works with cameras, video files, and streams.

Usage considerations include ensuring appropriate codecs and backends are installed, accounting for device variability and latency, handling errors gracefully, and selecting suitable fourcc codes, frame sizes, and frame rates to meet application requirements. Videoio remains a foundational layer for real-time video processing and multimedia applications.