Codecs

Codecs are software or hardware components that compress and decompress digital media data, enabling efficient storage and transmission. The term combines coder and decoder. A codec may function as an encoder, which reduces data size, and as a corresponding decoder, which reconstructs the original or a close approximation during playback. In practice, codecs are used with containers to package the coded streams and metadata.

Codecs are broadly categorized by quality and distortion characteristics into lossy and lossless. Lossless codecs reproduce the exact input data (for example FLAC for audio, ALAC). Lossy codecs discard some information to achieve higher compression (for example MP3, AAC for audio; H.264, HEVC for video). Many codecs use a combination of models, such as transform coding, perceptual models, and entropy coding, to reduce redundancy.

Common audio codecs: MP3, AAC, Opus, Vorbis, FLAC, ALAC. Common video codecs: H.264/AVC, H.265/HEVC, VP9, AV1. Open, royalty-free options include Opus, Vorbis, FLAC, AV1; patents affect licensing for MP3, AAC, H.264/HEVC in many markets.

Codecs operate inside containers that carry the encoded streams along with timing and metadata. Examples of containers include MP4, MKV, and WebM. The choice of codec affects bitrate, quality, latency, compatibility, and CPU load, influencing streaming, broadcast, and interactive communication.