A codec is an algorithm or program that compresses (encodes) video for storage or transmission and decompresses (decodes) it for playback. The word is a portmanteau of encoder and decoder. Common video codecs include H.264, H.265, and AV1, each offering different tradeoffs between compression efficiency, processing demand, and image quality. Choosing the right codec is a foundational decision in any live streaming system, as it determines bandwidth requirements and device compatibility.