MPEG-4 Part 2

MPEG-4 Part 2, MPEG-4 Visual (formally ISO/IEC 14496-2) is a video compression format developed by MPEG. It belongs to the MPEG-4 ISO/IEC standards. It is a discrete cosine transform compression standard, similar to previous standards such as MPEG-1 Part 2 and H.262/MPEG-2 Part 2. Several popular codecs including DivX, Xvid and Nero Digital implement this standard.

Note that MPEG-4 Part 10 defines a different format from MPEG-4 Part 2 and should not be confused with it. MPEG-4 Part 10 is commonly referred to as H.264 or AVC, and was jointly developed by ITU-T and MPEG.

MPEG-4 Part 2 is H.263 compatible in the sense that a basic H.263 bitstream is correctly decoded by an MPEG-4 Video decoder. (MPEG-4 Video decoder is natively capable of decoding a basic form of H.263.) In MPEG-4 Visual, there are two types of video object layers: the video object layer that provides full MPEG-4 functionality, and a reduced functionality video object layer, the video object layer with short headers (which provides bitstream compatibility with base-line H.263). MPEG-4 Part 2 is partially based on ITU-T H.263. The first MPEG-4 Video Verification Model (simulation and test model) used ITU-T H.263 coding tools together with shape coding.

To address various applications ranging from low-quality, low-resolution surveillance cameras to high definition TV broadcasting and DVDs, many video standards group features into profiles and levels. MPEG-4 Part 2 has approximately 21 profiles, including profiles called Simple, Advanced Simple, Main, Core, Advanced Coding Efficiency, Advanced Real Time Simple, etc. The most commonly deployed profiles are Advanced Simple and Simple, which is a subset of Advanced Simple.

Most of the video compression schemes standardize the bitstream (and thus the decoder) leaving the encoder design to the individual implementations. Therefore, implementations for a particular profile (such as DivX or Nero Digital which are implementations of Advanced Simple Profile and Xvid that implements both profiles) are all technically identical on the decoder side. A point of comparison would be that an MP3 file can be played in any MP3 player, whether it was created through iTunes, Windows Media Player, LAME or the common Fraunhofer encoder.

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