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MPEG has standardized the following compression formats and ancillary standards:

• MPEG-1: Initial video and audio compression standard. Later used as the standard for Video CD, and includes the popular Layer 3 ( MP3) audio compression format.
• MPEG-2: Transport, video and audio standards for broadcast-quality television. Used for over-the-air digital television ATSC and DVB, digital satellite TV services like DirecTV, digital cable television signals, and (with slight modifications) for DVD video discs.
• MPEG-3: Originally designed for HDTV, but abandoned when it was discovered that MPEG-2 was sufficient for HDTV.
• MPEG-4: Expands MPEG-1 to support video/audio "objects", 3D content, low bitrate encoding and support for Digital Rights Management. A new (newer than MPEG-2 Video) higher efficiency video codec is included (an alternative to MPEG-2 Video), see H.264.
• MPEG-7MPEG-7 is a multimedia content description standard. Thus, it is not a standard which deals with the actual coding of moving pictures and audio, like MPEG-1, MPEG-2 and MPEG-4. It uses XML to store metadata, and can be attached to timecode in order to tag: A formal system for describing multimedia content.
• MPEG-21The MPEG-21 standard, from the Moving Picture Experts Group aims at defining an open framework for multimedia applications. See also Digital Rights Management External links .: MPEG describes this future standard as a Multimedia Framework .

1 How MPEG works

The MPEG codecs use lossy data compressionA lossy data compression method is one where compressing a file and then decompressing it retrieves a file that may well be different to the original, but is "close enough" to be useful in some way. This type of compression is used a lot on the Internet a using transform codec s. In lossy transform codecs, samples of picture or sound are taken, chopped into small segments, transformed into a frequency space, and quantizedSignal processing In digital signal processing, quantization is the process of approximating a continuous signal by a set of discrete symbols or integer values; that is, converting an analog signal to a digital one. In general, a quantization operator can. The resulting quantized values are then entropy coded.

The moving picture coding systems such as MPEG-1, MPEG-2, and MPEG-4 add an extra step, where the picture content is predicted from past reconstructed images before coding, and only the differences from the reconstructed pictures, and any extra information needed to perform the prediction, are coded.

MPEG standardizes only the bitstream format and the decoder. The encoder is not standardized in any way but there are reference implementations available for members that produce valid bitstreams. That means that any MPEG-4 decoder can decode any MPEG-4 material (of the same type) regardless of the encoder which produced that material.