What compresses and decompresses video and audio?

• A. Encoder
• B. Container
• C. Codec
• D. Bitrate

Answer: (C)

The thing that compresses and decompresses video and audio is a codec. A codec defines the algorithm for reducing data size (encoding or compressing) and the corresponding method to restore it (decoding or decompressing). In practice, codecs come with both an encoder and a decoder as a paired system, so the same technology that creates the smaller stream is also capable of reconstructing the original when playing back. A container, on the other hand, is just a wrapper that holds the encoded streams, timing information, and metadata; it doesn’t perform compression. Bitrate is a measure of how much data is used per second, which influences quality and file size but isn’t the process that compresses or decompresses. For example, H.264 or H.265 are video codecs, and AAC is an audio codec; MP4 might be used to contain their compressed streams.