MPEG-4 Part 2
From Wikipedia, the free encyclopedia
MPEG-4 is a suite of standards which has many "parts", where each part standardizes various entities related to multimedia, like audio (part 3), video (parts 2 and 10), file formats (parts 12, 14 and 15). To know more about various parts and what they mean, please see the entry for MPEG-4.
MPEG-4 Part 2 is a video compression technology developed by MPEG, and now many documents simply refer to this as MPEG-4 video. It belongs to the MPEG-4 ISO/IEC standard (ISO/IEC 14496-2). The other common video codec defined as part of the MPEG-4 Standard, MPEG-4 part 10, is commonly referred to as H.264, and was jointly developed by ITU-T and MPEG.
MPEG-4 Visual is essentially still a Discrete Cosine Transform (DCT) compression standard, similar to previous standards such as MPEG-1 and MPEG-2.
Like the Audio components of MPEG-4, the video components are divided into several profiles that are aimed for use in several different standards. Most of the video compression schemes standardize the bitstream (and thus the decoder) leaving the encoder design to the individual implementations.
To address various applications starting with low quality, low bit rate and low resolution surveillance cameras (or mobile streaming) 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.
Contents |
[edit] Simple Profile
Simple Profile is mostly aimed for use in situations where low bit rate and low resolution are mandated by other conditions of the applications, like network bandwidth, device size etc etc. Examples are cell phones, some low end video conferencing systems, surveillance systems etc.
[edit] Advanced Simple Profile (ASP)
Advanced Simple Profile 's notable technical features relative to the Simple Profile, which is roughly similar to H.263, include:
- Support for "MPEG"-style quantization
- Support for interlaced video
- Support for B pictures
- Quarter-sample motion compensation (QPel)
- Global motion compensation (GMC)
The MPEG quantization and interlace support are designed in basically similar ways to the way it is found in MPEG-2 Part 2. The B picture support is designed in a basically similar way to the way it is found in MPEG-2 Part 2 and H.263v2.
The quarter-pixel motion compensation feature of ASP was innovative, and was later also included (in somewhat different forms) in MPEG-4 Part 10 and VC-1. Some implementations omit support for this feature, because it has a significantly harmful effect on speed and it is not always beneficial for quality.
The global motion compensation feature is not actually supported in most implementations although the standard officially requires decoders to support it. Most encoders do not support it either, and some experts say that it does not ordinarily provide any benefit in compression. When used, ASP's global motion compensation has a large unfavorable impact on speed and adds considerable complexity to the implementation.
[edit] See also
[edit] External links
| Multimedia compression formats | ||||||
|---|---|---|---|---|---|---|
| Video compression formats | ISO/IEC | MPEG-1 | MPEG-2 | MPEG-4 | MPEG-4/AVC | ITU-T | H.261 | H.262 | H.263 | H.264 | Others | AVS | Dirac | Indeo | MJPEG | RealVideo | VC-1 | Theora | VP6 | VP7 | WMV |
| Audio compression formats | ISO/IEC MPEG | MPEG-1 Layer III (MP3) | MPEG-1 Layer II | AAC | HE-AAC | ITU-T | G.711 | G.722 | G.722.1 | G.722.2 | G.723 | G.723.1 | G.726 | G.728 | G.729 | G.729.1 | G.729a | Others | AC3 | ATRAC | FLAC | iLBC | Monkey's Audio | Musepack | RealAudio | SHN | Speex | Vorbis | WavPack | WMA |
| Image compression formats | ISO/IEC/ITU-T | JPEG | JPEG 2000 | JPEG-LS | JBIG | JBIG2 | -- | -- | Others | BMP | GIF | ILBM | PCX | PNG | TGA | TIFF | WMP |
| Media container formats | General | 3GP | ASF | AVI | FLV | Matroska | MP4 | MXF | NUT | Ogg | Ogg Media | QuickTime | RealMedia | Audio only | AIFF | AU | WAV | -- | -- |
