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Video Codecs Explained

Confused over codecs? Feel like you're the only one who doesn't know MPEG-2 from MPEG-4? Your secret is safe with us. Just read this complete guide to today's video codecs and you'll be talking like an expert.

This article is an excerpt from Real World Video Compression, written by Andy Beach and just published by Peachpit Press. It's a truly outstanding book for online video newcomers and veterans alike.

A Webopedia.com Definition

codec: (1) Short for compressor/decompressor, a codec is any technology for compressing and decompressing data. Codecs can be implemented in software, hardware or a combination of both. Some popular codecs for computer video include MPEG, Indeo and Cinepak.

Descriptions of the Commonly Used Codecs

A variety of codecs can be implemented with relative ease on PCs and in consumer electronics equipment. It's therefore possible for multiple codecs to be available in the same product, avoiding the need to choose a single dominant codec for compatibility reasons. In the end, it seems unlikely that one codec will ever supplant all others.

Current Popular Codecs

The following sections cover some widely used video codecs, starting with the ones that are currently most popular, followed by a chronological-order list of the ones specified in international standards.

MPEG-4 part 10/H.264/AVC

MPEG-4 part 10 is a standard technically aligned with the ITU-T.s H.264 and often also referred to as AVC. This new standard is the current state of the art of ITU-T and MPEG standardized compression technology, and it is rapidly gaining adoption into a wide variety of applications. It uses different profiles and levels to identify different configurations and uses. It contains a number of significant advances in compression capability, and it has recently been adopted into a number of company products, including the Xbox 360, PlayStation Portable, iPod, the Nero Digital product suite, and Mac OS X 10.4, as well as high-definition Blu-ray Disc. Though it has impressive quality at bit rates lower than older codecs like MPEG-2, it is very processor-intensive to edit, encode, and play back, and older computers or low-powered portable devices may have difficulty playing it back or may drain their batteries faster than normal when using it.

VP6

This is a proprietary video codec developed by On2 Technologies and used in Adobe Flash Player 8 and newer.

VC-1

This is an SMPTE standardized video compression standard (SMPTE 421M) based on Microsoft.s WMV 9 video codec. It is also one of the three mandatory video codecs in Blu-ray high-definition optical disc standards (MPEG-2 and H.264 are the others). It is commonly found on the Web, in portable devices, and on computers that support the WMV format. Like MPEG-4 part 10, VC-1 uses the concept of profiles to differentiate different uses and data settings it will support though its configurations are more straightforward than MPEG-4 part 10/AVC/H.264.

MPEG-2 part 2

Used on DVD, on SVCD, and in most digital video broadcasting and cable distribution systems, MPEG-2.s sweet spot in the market is the quality of video it provides for standard-definition video. When used on a standard DVD, it offers good picture quality and supports wide-screen. In terms of technical design, the most significant enhancement in MPEG-2 over its predecessor, MPEG-1 (see the next section), was the addition of support for interlaced video. MPEG-2 is now considered an aged codec, but it has tremendous market acceptance and a very large installed base, and even the relatively new high-definition video acquisition format, HDV, is based on MPEG-2. Its use will decline as a delivery format as more efficient codecs such as AVC and VC-1 are adopted for HD video.

The Rest of the Pack

Plenty of other codecs are available. Some are older versions of the popular standards; others are geared toward specific uses so may not be as well known. Although you may not use or need many of these in your work, it.s good to know the names and backgrounds of what.s available. Many codecs have such similar names that it.s easy to get them confused.

H.261

Used primarily in older videoconferencing and video telephony products, H.261, developed by the ITU-T, was the first practical digital video compression standard. Essentially all subsequent standard video codec designs are based on it. It included such well-established concepts as YCbCr color representation, the 4:2:0 sampling format, 8-bit sample precision, 16 by 16 macroblocks, block-wise motion compensation, 8 by 8 block-wise discrete cosine transformation, zigzag coefficient scanning, scalar quantization, run+value symbol mapping, and variable length coding. H.261 supported only progressive scan video.

MPEG-1 part 2

This is used for video CDs (VCD) and also sometimes for online video. The quality is roughly comparable to that of VHS. If the source video quality is good and the bit rate is high enough, VCD can look better than VHS, but VCD requires high bit rates for this. MPEG-1 offers high compatibility, in that almost any computer can play back MPEG-1 files, and many DVD players also support the VCD format. However, it is an antiquated format that has been surpassed in terms of quality and file size by many others. MPEG-1 supports only progressive scan video.

DV

The DV codec, in terms of file-based content (as opposed to tape), has two main versions: DV-NTSC, the 720 by 480-pixel default DV codec comes installed with QuickTime for use in accordance with the North American broadcast standard and 720 by 576 DV-PAL is also available for European playback standards.

Avid DV (the other version of DV)

This is considered one of the best (if not the best) DV codecs available. Previous versions were tied to an Avid dongle, but the company has decided to cut the codec free, making it available to anyone wanting to install and use it.

Cineform

This is a high-quality production codec that works on both Mac and PCs and can scale from standard-definition to 4k film resolution. Cineform is a wavelet codec (not a DCT codec) that.s often used as a digital intermediary codec for editing video captured in formats like HDV that, because of the way they.re compressed, are difficult to edit on many systems.

H.263

Used primarily for videoconferencing, video telephony, and Internet video, H.263 represented a significant step forward in standardized compression capability for progressive scan video. Especially at low bit rates, it can provide a substantial improvement in the bit rate needed to reach a given level of fidelity.

MPEG-4 part 2

An MPEG standard that can be used for Internet, broadcast, and on-storage media, MPEG-4 part 2 offers improved quality relative to MPEG-2 and the first version of H.263. Its major technical features beyond prior codec standards consisted of object-oriented coding features and a variety of other such features not necessarily intended for the improvement of ordinary video-coding compression capability. It also included some enhancements of compression capability, both by embracing capabilities developed in H.263 and by adding new ones such as quarter pixel motion compensation. Like MPEG-2, it supports both progressive scan and interlaced video.

DivX, Xvid, FFmpeg MPEG-4, and 3ivx

These are different implementations of MPEG-4 part 2.

Sorenson 3

This is a codec that was popularly used by Apple Quick- Time prior to the launch of H.264. Many of the QuickTime movie trailers found on the Web use this codec.

Sorenson Spark

This is a codec that was licensed to Macromedia for use in its Flash Player 6. This is in the same family as H.263.

Theora

Developed by the Xiph.org Foundation as part of its Ogg project, based upon On2 Technologies. VP3 codec, and christened by On2 as the successor in VP3.s lineage, Theora was designed to compete with MPEG-4 video and similar lower-bit rate video compression schemes.

RealVideo

Developed by RealNetworks, this was a popular codec in the late 1990s and early 2000s but is now fading in importance as newer codecs have evolved and because of a lack of recent updates to its quality and performance.

Cinepak

A very early codec used by Apple.s QuickTime, Cinepak was very popular with interactive CD-ROM authors in the mid 1990s.

x264

A GPL-licensed implementation of H.264 encoding standard, x264 is only an encoder.

Huffyuv

Huffyuv (or HuffYUV) is a very fast, lossless Win32 video codec written by Ben Rudiak-Gould and published under the terms of the GPL as free software, meant to replace uncompressed YCbCr as a video capture format. A more up-to-date version of Huffyuv is also available called Lagarith.

SheerVideo

A family of fast, lossless QuickTime and AVI codecs developed by BitJazz, SheerVideo is a production-based codec that is popular because of its support of Y.CbCr 4:4:4 and 4:2:2 formats, for both 10-bit and 8-bit channels, and for both progressive and interlaced data. It is also available for both Mac and PC, making it ideal for cross platform production environments.

This article originally appeared on WebVideoUniverse.com. Excerpted from Real World Video Compression by Andy Beach (Peachpit Press)







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