MPEG-4 Part 2
MPEG-4 Part 2, MPEG-4 Visual (formally ISO/IEC 14496-21) is a video compression technology 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.)234 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).5 MPEG-4 Part 2 is partially based on ITU-T H.263.6 The first MPEG-4 Video Verification Model (simulation and test model) used ITU-T H.263 coding tools together with shape coding.7
|Edition||Release date||Latest amendment||Standard||Description|
|First edition||1999||2000||ISO/IEC 14496-2:19999|
|Second edition||2001||2003||ISO/IEC 14496-2:200110|
|Third edition||2004||20091||ISO/IEC 14496-2:20041|
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.
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. Examples are mobile phones, some low end video conferencing systems, electronic surveillance systems etc.
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 (a.k.a. B-frames)
- Quarter Pixel 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.
The MPEG-4 Simple Studio Profile (SStP), or ISO/IEC 14496-2, has 6 levels going from SDTV to 4K resolution.11 MPEG-4 SStP allows for up to 12-bit bit depth and up to 4:4:4 chroma subsampling.11 MPEG-4 SStP is used by HDCAM SR.11
|Level||Max bit depth and
|Max resolution and frame rate||Max data rate (kbit/s)|
|2||10-bit 4:2:2||1920×1080 30p/60i||600,000|
|3||12-bit 4:4:4||1920×1080 30p/60i||900,000|
|4||12-bit 4:4:4||2K×2K 30p||1,350,000|
|5||12-bit 4:4:4||4K×2K 30p||1,800,000|
|6||12-bit 4:4:4||4K×2K 60p||3,600,000|
Despite being generally well received, MPEG-4 Part 2 has drawn some criticism. FFmpeg's maintainer Michael Niedermayer has criticised MPEG-4 for lacking an in-loop deblocking filter, GMC being too computationally intensive, and OBMC being defined but not allowed in any profiles among other things.12 Microsoft's Ben Waggoner states "Microsoft (well before my time) went down the codec standard route before with MPEG-4 part 2, which turns out to be a profound disappointment across the industry - it didn't offer that much of a compression advantage over MPEG-2, and the protracted license agreement discussions scared off a lot of adoption. I was involved in many digital media projects that wouldn't even touch MPEG-4 in the late '90s to early '00s because there was going to be a 'content fee' that hadn't been fully defined yet."13
- ISO. "ISO/IEC 14496-2:2004 - Information technology -- Coding of audio-visual objects -- Part 2: Visual". ISO. Retrieved 2009-11-01.
- chiariglione.org (2006-08-10). "Riding the Media Bits, End of the Ride?". Retrieved 2010-03-10.
- chiariglione.org (2003-10-25). "Riding the Media Bits, Inside MPEG-4 - Part B". Retrieved 2010-03-10.
- ISO/IEC JTC1/SC29/WG11 (2000-03). "MPEG-4 Video - Frequently Asked Questions". chiariglione.org. Retrieved 2010-03-10.
- Touradj Ebrahimi and Caspar Horne. "MPEG-4 Natural Video Coding - An overview". chiariglione.org. Retrieved 2010-03-10.
- chiariglione.org (2009-09-06). "Riding the Media Bits, The development of MPEG-1 - Part A". Retrieved 2010-03-10.
- Fernando Pereira. "MPEG-4: Why, What, How and When?". chiariglione.org. Retrieved 2010-03-10.
- MPEG. "MPEG standards - Full list of standards developed or under development". chiariglione.org. Retrieved 2009-10-31.
- ISO. "ISO/IEC 14496-2:1999 - Information technology -- Coding of audio-visual objects -- Part 2: Visual". ISO. Retrieved 2009-11-01.
- ISO. "ISO/IEC 14496-2:2001 - Information technology -- Coding of audio-visual objects -- Part 2: Visual". ISO. Retrieved 2009-11-01.
- Yasuhiko Mikami; Hugo Gaggioni. "4K End-to-End HPA Technology Retreat 2010" (PDF). Sony. Retrieved 2012-11-28.
- Lair Of The Multimedia Guru » 15 reasons why MPEG4 sucks
- VC-1 and H264 - Page 2 - Doom9's Forum
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