An audio codec is a compression algorithm specifically designed to encode and decode audio data within a video stream. Just as video codecs compress visual data, audio codecs reduce the file size of audio by removing frequencies and details that human hearing is less sensitive to. Common audio codecs in live streaming include AAC, which provides good quality at low bitrates and is the most widely supported, and Opus, which is optimized for real-time communications and used in WebRTC-based streaming.