A codec is a software or hardware component that is used to encode or decode audio or video data. Codecs are an essential part of audio and video playback, as they are responsible for compressing and decompressing the data in a way that allows it to be transmitted over a network or stored in a file. Codecs are often used in conjunction with media playback software, such as media players or web browsers, and are typically selected automatically based on the format and properties of the audio or video data. Different codecs can have different levels of efficiency and quality, and the choice of codec can have a significant impact on the overall performance and quality of the audio or video playback.