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Audio and video call for customized methods of compression. Engineers and Mathematicians have tried a number of solutions for tackling this problem. There is a complex balance between the Video Quality , the quantity of the data needed to represent it, also known as the bit rate, the complexity of the encoding and decoding algorithms, robustness to data losses and errors, ease of editing, random access, the state of the art of compression algorithm design, end-to-end delay, and a number of other factors. APPLICATIONS In daily life, digital video codecs are found in DVD (MPEG-2), VCD (MPEG-1), in emerging satellite and terrestrial broadcast systems, and on the Internet. Online video material is encoded in a variety of codecs, and this has led to the availability of codec packs - a pre-assembled set of commonly used codecs combined with an installer available as a software package for PCs. Encoding media by the public has seen an upsurge with the availability of DVD-writers. Since commercially available DVDs are usually dual-layer, and hence bigger than the more common single layer writable DVDs, it is often the case that the material has to be compressed again, sacrificing quality so that the media will fit onto a single disc. VIDEO CODEC DESIGN Video codecs seek to represent a fundamentally analog data set in a digital way. Because of the design of analog video signals, which represent . Different codecs will use different standard uses 4:1:1 sampling ratios. Professional video codecs designed to function at much higher bitrates and to record a greater amount of color information for post-production manipulation sample in 3:1:1 (uncommon), 4:2:2 and 4:4:4 ratios. Examples of these codecs include Panasonic's DVCPRO50 and DVCPROHD codecs (4:2:2), and then Sony's HDCAM-SR (4:4:4) or Panasonic's HDD5 (4:2:2). Apple's new Prores HQ 422 codec also samples in 4:2:2 color space. More codecs that sample in 4:4:4 patterns exist as well, but are less common, and tend to be used internally in post-production houses. It is also worth noting that video codecs can operate in RGB space as well. These codecs tend not to sample the red, green, and blue channels in different ratios, since there is no perceptual motivation for doing so. Some amount of spatial and temporal Downsampling may also be used to reduce the raw data rate before the basic encoding process. The most popular such transform is the 8x8 Discrete Cosine Transform (DCT). Codecs which make use of a Wavelet transform are also entering the market, especially in camera workflows which involve dealing with RAW image formatting in motion sequences. The output of the transform is first Quantized , then Entropy Encoding is applied to the quantized values. When a DCT has been used, the coefficients are typically scanned using a zig-zag scan order, and the entropy coding typically combines a number of consecutive zero-valued quantized coefficients with the value of the next non-zero quantized coefficient into a single symbol, and also has special ways of indicating when all of the remaining quantized coefficient values are equal to zero. The entropy coding method typically uses Variable-length Coding Tables . Some encoders can compress the video in a multiple step process called ''n-pass'' encoding (e.g. 2-pass), which performs a slower but potentially better quality compression. The decoding process consists of performing, to the extent possible, an inversion of each stage of the encoding process. The one stage that cannot be exactly inverted is the Quantization stage. There, a best-effort approximation of inversion is performed. This part of the process is often called "inverse quantization" or "dequantization", although quantization is an inherently non-invertible process. This process involves representing the video image as a set of Macroblocks . For more information about this critical facet of video codec design, see B Pictures . Video codec designs are often standardized or will be in the future- i.e., specified precisely in a published document. However, only the decoding process needs to be standardized to enable interoperability. The encoding process is typically not specified at all in a standard, and implementers are free to design their encoder however they want, as long as the video can be decoded in the specified manner. For this reason, the quality of the video produced by decoding the results of different encoders that use the same video codec standard can vary dramatically from one encoder implementation to another. COMMONLY USED STANDARDS AND CODECS A variety of codecs can be implemented with relative ease on PCs and in consumer electronics equipment. It is 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 replace them all. Some widely-used video codecs are listed below, starting with a chronological-order list of the ones specified in International Standard s. ''', 8x8 block-wise Discrete Cosine Transform ation, zig-zag coefficient scanning, Scalar Quantization , run+value symbol mapping, and Variable-length Coding . H.261 supported only Progressive Scan video.
''', SVCD , and in most digital video broadcasting and cable distribution systems. When used on a standard DVD, it offers good picture quality and supports widescreen. When used on SVCD, it is not as good as DVD but is certainly better than VCD. In terms of technical design, the most significant enhancement in MPEG-2 relative to MPEG-1 was the addition of support for Interlace d video. MPEG-2 is now considered an aged codec, but has tremendous market acceptance and a very large installed base. ''' video. Especially at low bit rates, it could provide a substantial improvement in the bit rate needed to reach a given level of fidelity. ''' standard that can be used for internet, broadcast, and on storage media. It 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 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-pel Motion Compensation . Like MPEG-2, it supports both Progressive Scan and Interlace d video. MPEG-4 Part 10 (a technically aligned standard with the ITU-T 's ''' H.264 ''' and often also referred to as '''AVC'''). This emerging new standard is the current state of the art of ITU-T and MPEG standardized compression technology, and is rapidly gaining adoption into a wide variety of applications. It contains a number of significant advances in compression capability, and it has recently been adopted into a number of company products, including for example the XBOX 360 , PlayStation Portable , IPod , the Nero Digital product suite, Mac OS X V10.4 , as well as HD DVD / Blu-ray Disc . DivX , ''' Xvid ''', ''' FFmpeg MPEG-4''' and ''' 3ivx ''': Different implementations of MPEG-4 Part 2. VP6 : A proprietary video codec developed by On2 Technologies and used in Adobe Flash Player 8 and above. ''', basically the ancestor of H.264 . Many of the QuickTime movie trailers found on the web use this codec. '''. ''' as part of their Ogg project, based upon On2 Technologies' VP3 codec, and christened by On2 as the successor in VP3's lineage, Theora is targeted at competing with MPEG-4 video and similar lower-bitrate video compression schemes. ''''s family of video codec designs including WMV 7, WMV 8, and WMV 9. It can do anything from low resolution video for dial up internet users to HDTV . The latest generation of WMV is standardized by SMPTE as the VC-1 standard. '''9 video codec. One of the 3 mandatory video codecs in both HD-DVD and Blu-Ray high-definition optical disc standards. Commonly found in portable devices and on streaming video websites in its Windows Media Video implementation. '''. A popular codec technology a few years ago, now fading in importance for a variety of reasons. Cinepak : A very early codec used by Apple's QuickTime. 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. See Lagarith as a more up-to-date codec. Lagarith : A more up-to-date fork of Huffyyuv is available as Lagarith. SheerVideo : A family of ultrafast lossless QuickTime and AVI codecs, developed by BitJazz Inc., for RGB Y'CbCr[A 4:4:4 Y'CbCr[A and 4:2:2[:4] formats; for both 10-bit and 8-bit channels; for both progressive and interlaced data; for both Mac and PC. All of the codecs above have their qualities and drawbacks. Comparisons are frequently published. The tradeoff between compression power, speed, and fidelity (including Artifacts ) is usually considered the most important figure of technical merit. MISSING CODECS AND VIDEO FILE ISSUES A common problem when an end user wants to watch a video stream encoded with a specific codec is that if the exact codec is not present and properly installed on the user's machine, the video won't play (or won't play optimally). Windows XP SP2 itself only has a very limited number of video and audio codecs installed; other than Microsoft formats, Intel Indeo is the only available .avi Codec that is installed per default. All other codecs, such as DivX, Xvid or Theora, must be installed manually. List of the available/default codecs after a Windows XP SP2 Installation Some video files and codec analysis tools have been made available to provide a user-friendly way to solve this common problem: VideoInspector : Analyzes most containers (AVI, Matroska, MPEG, etc.) and gives direct download links for missing codecs. GSpot : A pioneer in troubleshooting video applications, GSpot remains a useful tool despite missing some features present in other software. MediaInfo : Open-source alternative to GSpot. AVICodec : Another useful application. AVI2Clipboard : An extension for the Explorer context menu to easily view and save information about videos with an AVI container. Many people find that VLC Media Player resolves many of these issues because it contains many popular codecs in a portable standalone library, available for many Operating Systems , including Windows, Linux, and Mac OS X. This also resolves many issues within Windows in conflicting and poorly installed codecs. VIDEO CODEC BENCHMARKING For directshow users who are interested in their benchmarking their video decoders try using the Haali TimeCodec . It requires that you install the latest version of the Haali Media Splitter before using it. Another method is using the internal audio and video decoders built into TCPMP for both mobile devices and desktop PC's. See Shinos TCPMP benchmark page SEE ALSO
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