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For instance, many multimedia data streams need to contain both audio and video data, and often some form of metadata that permits synchronization of the audio and video. Each of these three pieces of data may be handled by different programs, processes, or hardware; but for the multimedia data stream to be useful in stored or transmitted form, they must be encapsulated together.
The raw encoded form of audio and video data is often called essence, to distinguish it from the metadata information that together make up the information content of the stream, and any "wrapper" data that is then added to aid access to or improve the robustness of the stream.
Some examples of codecs include the following:
See also: multimedia compression, Digital signal processing, Audio signal processing, Lossy data compression