- Comparison of video codecs
The compression may employ lossy data compression, so quality measurement issues become important. Shortly after the compact disc became widely available as a digital-format replacement for analog audio, it became feasible to also store and use video in digital form. A variety of technologies soon emerged to do so. The primary goal for most methods of compressing video is to produce video that most closely approximates the fidelity of the original source and simultaneously deliver the smallest file size possible. However, there are also several other factors that can be used as a basis for comparison.
- 1 Introduction to comparison
- 2 Video quality
- 3 Performance comparison
- 4 Software characteristics
- 5 Freely available codecs comparisons
- 6 See also
- 7 Notes and references
- 8 External links
Introduction to comparison
The following characteristics are compared in video codecs comparisons:
- Video quality per bitrate (or range of bitrates). Commonly video quality is considered the main characteristic of codec comparisons. Video quality comparisons can be subjective or objective.
- Performance characteristics like compression/decompression speed, supported profiles/options, supported resolutions, supported rate control strategies etc.
- General software characteristics, for example:
The quality the codec can achieve is heavily based on the compression format the codec uses. A codec is not a format, and there can be multiple codecs that implement the same compression specification – for example, MPEG-1 codecs typically do not achieve quality/size ratio comparable to codecs that implement the more modern H.264 specification. But quality/size ratio of output produced by different implementations of the same specification can vary, too.
Prior to comparing codec video quality, it is important to understand that every codec can give a varying degree of quality for a given set of frames within a video sequence. Numerous factors play a role in this variability. First, all codecs have a bitrate control mechanism which is responsible for determining the bitrate and quality on a per-frame basis. A difference between variable bit rate (VBR) and constant bit rate (CBR) creates a trade-off between a consistent quality over all frames, and a more constant bitrate, which is required for some applications. Second, some codecs differentiate between different types of frames such as key frames and non-key frames, differing in their importance to overall visual quality and the extent to which they can be compressed. Third, quality depends on prefiltrations, that is included on all present-day codecs. Other factors can also come into play.
For a sufficiently long clip, it is possible to select sequences which have suffered little from the compression and sequences which have suffered heavily, especially if CBR was used, in which the quality between frames can vary highly due to different amounts of compression needed to achieve a constant bitrate. So, in any one long clip such as a full length movie, any two codecs may perform quite differently on a particular sequence from the clip, while the codecs may be approximately equal (or the situation reversed) in quality over a wider sequence of frames. Press-releases and amateur forums sometimes select sequences known to favor a particular codec or style of rate control in reviews.
Objective video quality
Objective video evaluation techniques are mathematical models that approximate results of subjective quality assessment, but are based on criteria and metrics that can be measured objectively and automatically evaluated by a computer program. Objective methods are classified based on the availability of the original video signal, which is considered to be of high quality (generally not compressed). Therefore, they can be classified as:
- Full reference methods (FR), where the whole original video signal is available
- Reduced reference methods (RR), where only partial information of the original video is available, and
- No-reference methods (NR), where the original video is not available at all.
The main FR metrics are:
- Peak signal-to-noise ratio (PSNR)
- The most widely used video quality metric during the last 20 years (used approximately in 99% of scientific papers and in 20% of marketing materials). However, the validity of this metric is limited. It is only conclusive when the same codec (or codec type) and content is being compared.
- Structural similarity (SSim.)
- A new metric (suggested in 2004) which shows better results than PSNR at the cost of a reasonable increase in computational complexity.
- VQuad-HD an ITU-T J.341 standard
- The new standard was recently (Jan 2011) approved by ITU-T as J.341. The new VQuad-HD™ algorithm was developed by Swissqual in 2008-2010. It was the best performing model in the HDTV competition to find the new standard that was organized by the independent and non-commercial Video Quality Expert Group (VQEG).More information on VQuad-HD can be found in the technical white paper "Video Quality Measurement for High Definition Video Signals" available for download from: white paper
Some other metrics have been suggested by Video Quality Experts Group (VQEG), private companies, and universities, but are not widespread.
The main comparison method is the so-called RD-curve (rate/distortion chart), where a metric value is plotted against the Y-axis and the bitrate against the X-axis.
Some example NR metrics are:
- Blocking measure — measurement power of so called blocking artefacts (extremely noticeable without deblocking filter usage on low bitrates)
- Blurring measure — measurement of common video blurring (washout)
Subjective video quality
It is concerned with how video is perceived by a viewer and designates his or her opinion on a particular video sequence. Subjective video quality tests are quite expensive in terms of time (preparation and running) and human resources.
There is an enormous number of ways of showing video sequences to experts and of recording their opinions. A few of them have been standardized. They are thoroughly described in ITU-R recommendation BT.500.
Following subjective video quality comparison methods are used:
- Double Stimulus Impairment Scale (DSIS) — suggested in ITU-R BT.500-11.
- Double Stimulus Continuous Quality Scale (DSCQS) type I and type II — suggested in ITU-R BT.500-11
- Stimulus Comparison Adjectival Categorical Judgement (SCACJ) — suggested in ITU-R BT.500-11
- Subjective Assessment Method for Video Quality evaluation (SAMVIQ)
- MSU Continuous Quality Evaluation (MSUCQE)
The reason for measuring subjective video quality is the same as for measuring the Mean Opinion Score for audio. Opinions of experts can be averaged; average mark is usually given with confidence interval. Additional procedures can be used for averaging, for example experts who give unstable results can be rejected (for instance, if their correlation with average opinion is small).
In case of video codecs, this is a very common situation. When codecs with similar objective results show results with different subjective results, the main reasons can be:
- Pre- and postfilters are widely used in codecs. Commonly codecs use prefilters like video denoising, deflicking, deshacking, etc. Denoising and deflicking commonly maintain PSNR value, but increase visual quality (the best slow denoising filters also increase PSNR on middle and high bitrates). Deshacking seriously decreases PSNR, but increases visual quality. The same situation with postfilters — deblocking and deringing maintain PSNR, but increase quality. Graining (suggested in H.264) essentially increases video quality especially on big plasma screens, but decrease PSNR.
- Note: All filters worsen compression/decompression time, so they increase visual quality, but decrease speed.
- Motion estimation (ME) search strategy can also cause different visual quality for the same PSNR. So called true motion search commonly will not reach minimum sum of absolute differences (SAD) values in codec ME, but may result in better visual quality. Also such methods require more compression time.
- Rate control strategy. VBR commonly cause better visual quality marks than CBR for the same average PSNR values for sequences.
It is difficult to use long sequences for subjective testing. Commonly, three or four ten-second sequences are used, compared with full movies used for objective metrics. Sequence selection is important — those sequences that are similar to the ones used by developers to tune their codecs are more competitive.
Number of frames per second (FPS) commonly used for compression/decompression speed measurement.
The following issues should be considered when estimating probable codec performance differences:
- Decompression (sometimes compression) frame time uniformity. Big differences in this value can cause annoying jerkily playback.
- SIMD support by processor and codec — e.g., MMX, SSE, SSE2, each of which change CPU performance on some kinds of tasks (often including those with which codecs are concerned).
- Multi-threading support by processor and codec (sometimes turning on Hyper-threading support (if available on a particular CPU) causes codec speed to decrease)
- RAM speed (generally important for most codec implemenations)
- Processor cache size (low values sometimes cause serious speed degradation, e.g. for CPUs with low cache such as several of the Intel Celeron series.)
- GPU usage by codec — some codecs can drastically increase their performance by taking advantage of GPU resources.
So, for example, codec A (being optimized for memory usage, i.e. uses less memory) may give slower performance on modern computers (which are typically not memory limited) than codec B. The same pair of codecs may give opposite results if running on an older computer with reduced memory (or cache) resources.
Modern standards define a wide range of features and require very substantial software or hardware efforts and resources for their implementation. Only selected profiles of a standard are typically supported in any particular product. (This very common situation for H.264 implementations for example.)
The H.264 standard includes the following seven sets of capabilities, which are referred to as profiles, targeting specific classes of applications:
- Baseline Profile (BP): Primarily for lower-cost applications with limited computing resources, this profile is used widely in videoconferencing and mobile applications.
- Main Profile (MP): Originally intended as the mainstream consumer profile for broadcast and storage applications, the importance of this profile faded when the High profile was developed for those applications.
- Extended Profile (XP): Intended as the streaming video profile, this profile has relatively high compression capability and some extra tricks for robustness to data losses and server stream switching.
- High Profile (HiP): The primary profile for broadcast and disc storage applications, particularly for high-definition television applications (this is the profile adopted into HD DVD and Blu-ray Disc, for example).
- High 10 Profile (Hi10P): Going beyond today's mainstream consumer product capabilities, this profile builds on top of the High Profile — adding support for up to 10 bits per sample of decoded picture precision.
- High 4:2:2 Profile (Hi422P): Primarily targeting professional applications that use interlaced video, this profile builds on top of the High 10 Profile — adding support for the 4:2:2 chroma sampling format while using up to 10 bits per sample of decoded picture precision.
- High 4:4:4 Predictive Profile (Hi444PP): This profile builds on top of the High 4:2:2 Profile — supporting up to 4:4:4 chroma sampling, up to 14 bits per sample, and additionally supporting efficient lossless region coding and the coding of each picture as three separate color planes.
- Multiview High Profile: This profile supports two or more views using both inter-picture (temporal) and MVC inter-view prediction, but does not support field pictures and macroblock-adaptive frame-field coding.
The standard also contains four additional all-Intra profiles, which are defined as simple subsets of other corresponding profiles. These are mostly for professional (e.g., camera and editing system) applications:
- High 10 Intra Profile: The High 10 Profile constrained to all-Intra use.
- High 4:2:2 Intra Profile: The High 4:2:2 Profile constrained to all-Intra use.
- High 4:4:4 Intra Profile: The High 4:4:4 Profile constrained to all-Intra use.
- CAVLC 4:4:4 Intra Profile: The High 4:4:4 Profile constrained to all-Intra use and to CAVLC entropy coding (i.e., not supporting CABAC).
Moreover, the standard now also contains three Scalable Video Coding profiles.
- Scalable Baseline Profile: A scalable extension of the Baseline profile.
- Scalable High Profile: A scalable extension of the High profile.
- Scalable High Intra Profile: The Scalable High Profile constrained to all-Intra use.
An accurate comparison of codecs must take the profile variations within each codec into account.
See also MPEG-2 Profiles and Levels.
Supported rate control strategies
Videocodecs rate control strategies can be classified as:
- Variable bit rate (VBR) and
- Constant bit rate (CBR).
Variable bit rate (VBR) is a strategy to maximize the visual video quality and minimize the bit rate. On fast motion scenes, a variable bit rate uses more bits than it does on slow motion scenes of similar duration yet achieves a consistent visual quality. For real-time and non-buffered video streaming when the available bandwidth is fixed, e.g. in videoconferencing delivered on channels of fixed bandwidth, a constant bit rate (CBR) must be used.
CBR is commonly used for videoconferences, satellite and cable broadcasting. VBR is commonly used for video CD/DVD creation and video in programs.
General video codec information — creator/company, license/price, etc. Codec Creator/Maintainer First public release date Latest stable version License Patented compression formats Compression method OpenCL support nVidia CUDA support ATI Stream/AMD APP support Intel AVX support Intel Quick Sync Video support libtheora (Theora) Xiph.org 2002-09-25 1.1.1 (2009) BSD-style Patented, but freely licensed[*] Lossy Unknown Unknown Unknown Unknown Unknown dirac-research (Dirac) BBC Research Department 2008-09-17 1.0.2 (2009) MPL 1.1, GNU GPL 2, GNU LGPL 2.1 none Lossy/lossless Unknown Unknown Unknown Unknown Unknown Schrödinger (Dirac) David Schleef 2008-02-22 1.0.9 (2010) MPL 1.1, GNU GPL 2, GNU LGPL 2, MIT License none Lossy/lossless Unknown Unknown Unknown Unknown Unknown x264 x264 team 2003 r2019 (2011) GNU GPL MPEG-4 AVC/H.264 Lossy/lossless No No No Partial Unknown Xvid Xvid team 2001 1.3.2 (2011) GNU GPL MPEG-4 ASP Lossy Unknown Unknown Unknown Unknown Unknown FFmpeg (libavcodec) FFmpeg team 2000 0.8.5 (2011) GNU LGPL MPEG-1, MPEG-2, MPEG-4 ASP, H.261, H.263, VC-3, WMV7, WMV8, MJPEG, MPEG-4v3, DV etc. Lossy/lossless Unknown Unknown Unknown Unknown Unknown FFavs (libavcodec) FFavs team 2009 0.0.3 GNU LGPL MPEG-1, MPEG-2, MPEG-4 ASP etc. Lossy/lossless Unknown Unknown Unknown Unknown Unknown Blackbird Forbidden Technologies plc 2006-01 2 Proprietary Blackbird Lossy Unknown Unknown Unknown Unknown Unknown DivX DivX, Inc. 2001 DivX Plus (2010) Proprietary MPEG-4 ASP, H.264 Lossy Unknown Unknown Unknown Unknown Unknown DivX a hack of Microsoft's MPEG-4v3 codec 1998 3.20 alpha (2000) Proprietary Microsoft's MPEG-4v3 (not MPEG-4 compliant) Lossy Unknown Unknown Unknown Unknown Unknown 3ivx 3ivx Technologies Pty. Ltd. 2001 5.0.2 (2007) Proprietary MPEG-4 ASP Lossy Unknown Unknown Unknown Unknown Unknown Nero Digital Nero AG 2003 Unknown Proprietary MPEG-4 ASP, H.264 Lossy Unknown Unknown Unknown Unknown Unknown ProRes 422 / ProRes 4444 Apple Inc. 2007 Proprietary Unknown Lossy Unknown Unknown Unknown Unknown Unknown Sorenson Video Sorenson Media 1998 Proprietary Sorenson Video Lossy Unknown Unknown Unknown Unknown Unknown Sorenson Spark Sorenson Media 2002 Proprietary Sorenson Spark Lossy Unknown Unknown Unknown Unknown Unknown VP3 On2 Technologies 2000 BSD-style Patented, but freely licensed[*] Lossy Unknown Unknown Unknown Unknown Unknown VP4 On2 Technologies 2001 Proprietary VP4 Lossy Unknown Unknown Unknown Unknown Unknown VP5 On2 Technologies 2002 Proprietary VP5 Lossy Unknown Unknown Unknown Unknown Unknown VP6 On2 Technologies 2003 Proprietary VP6 Lossy Unknown Unknown Unknown Unknown Unknown VP7 On2 Technologies 2005 Proprietary VP7 Lossy Unknown Unknown Unknown Unknown Unknown VP8 On2 Technologies (now owned by Google) 2008 BSD-style Patented, but freely licensed Lossy Unknown Unknown Unknown Unknown Unknown DNxHD Avid Technology 2008 Proprietary VC-3 Lossy Unknown Unknown Unknown Unknown Unknown Cinema Craft Encoder SP2 Custom Technology Corporation 2000 1.00.01.09 (2009) Proprietary MPEG-1, MPEG-2 Lossy Unknown Unknown Unknown Unknown Unknown TMPGEnc Free Version Pegasys Inc. 2001 2.525.64.184 (2008) Proprietary MPEG-1, MPEG-2 Lossy Unknown Unknown Unknown Unknown Unknown Windows Media Encoder Microsoft 1999 9 (2003) (WMV3 in FourCC) Proprietary WMV, VC-1, (in early versions MPEG-4 Part 2 and not MPEG-4 compliant MPEG-4v3, MPEG-4v2) Lossy Unknown Unknown Unknown Unknown Unknown Cinepak Created by SuperMac, Inc.
Currently maintained by Compression Technologies, Inc.
1991 126.96.36.199 (1999) Proprietary Unknown Lossy Unknown Unknown Unknown Unknown Unknown Indeo Video Intel Corporation, currently offered by Ligos Corporation 1992 5.2 Proprietary Indeo Video Lossy Unknown Unknown Unknown Unknown Unknown TrueMotion S The Duck Corporation 1995 Proprietary TrueMotion S Lossy Unknown Unknown Unknown Unknown Unknown RealVideo RealNetworks 1997 RealVideo 10 Proprietary H.263, RealVideo Lossy Unknown Unknown Unknown Unknown Unknown ACT-L3 Streambox 2003-02-21 3.4 (2009) Proprietary Unknown Lossy Unknown Unknown Unknown Unknown Unknown Huffyuv Ben Rudiak-Gould 2000 2.1.1 (2003) GNU GPL 2 none Lossless Unknown Unknown Unknown Unknown Unknown Lagarith Ben Greenwood 2004-10-04 1.3.26 (2011-09-25) GNU GPL 2 none Lossless Unknown Unknown Unknown Unknown Unknown MainConcept MainConcept GmbH 1993 8.8.0 (2011) Proprietary MPEG-1, MPEG-2, H.264/AVC, H.263, VC-3, MPEG-4 Part 2, DV, MJPEG etc. Lossy Yes Yes Unknown Unknown Yes Elecard Elecard 2008 G4 (2010) Proprietary MPEG-1, MPEG-2, MPEG-4, AVC Lossy Unknown Unknown Unknown Unknown Unknown
- The Xiph.Org Foundation has negotiated an irrevocable free license to Theora and other VP3-derived codecs for everyone, for any purpose.
Native operating system support
Note that operating system support does not mean whether video encoded with the codec can be played back on the particular operating system – for example, video encoded with the DivX codec is playable on Unix-like systems using free MPEG-4 ASP decoders (FFmpeg MPEG-4 or Xvid), but the DivX codec (which is a software product) is only available for Windows and Mac OS X.
Encoder Operating System Support Codec Mac OS X other Unix & Unix-like Windows 3ivx Yes Yes Yes Blackbird Yes Yes Yes Cinepak Yes No Yes DivX Yes No Yes FFmpeg Yes Yes Yes RealVideo Yes Yes Yes Schrödinger (Dirac) Yes Yes Yes Sorenson Video 3 Yes No Yes Theora Yes Yes Yes x264 Yes Yes Yes Xvid Yes Yes Yes Elecard No No Yes
Codec Compression type Basic algorithm Highest supported bitrate Highest supported resolution Variable frame rate Blackbird Lossy compression Unknown Unknown 384×288 (PAL), 320×240 (NTSC) Yes Cinepak Lossy compression Vector quantization Unknown Unknown Unknown Dirac Lossy/Lossless compression Wavelet compression Unlimited Unlimited Yes Sorenson 3 Lossy compression Unknown Unknown Unknown Unknown Theora Lossy compression Discrete cosine transform 2 Gibit/s 1,048,560×1,048,560 Via chaining[*] RealVideo Lossy compression Discrete cosine transform Unknown Unknown Yes Elecard Lossy compression Unknown Unlimited 16k Yes
- Theora streams with different frame rates can be chained in the same file, but each stream has a fixed frame rate.
Freely available codecs comparisons
List of freely available comparisons and their content description:
Name of comparison Type of comparison Date(s) of publication List of compared codecs Comments Series of Doom9 codec comparisons Series of subjective comparison of popular codecs
- DivX4.12, On2 VP3, XviD 1/25 and WMV8 and DivX5.01, XviD 3/27 and ON2 VP4 — at first version
- Dirac, Elecard AVC HP, libavcodec MPEG-4, NeroDigital ASP, QuickTime 7, Snow, Theora, VideoSoft H.264 HP, XviD 1.1 beta 2 — in last one
Subjective comparison with convenient visualization Series of MSU annual H.264 codecs comparisons Series of objective H.264 codecs comparisons with MPEG-4 ASP reference
- 2005 Jan.
- 2005 Dec.
- 2006 Dec.
- 2007 Dec.
- 2009 May
- 2010 Apr.
- 2005 (Jan.): Mpegable AVC, Moonlight H.264, MainConcept H.264, Fraunhofer IIS, Ateme MPEG-4 AVC/H.264, Videosoft H.264, DivX Pro 5.1.1 (Not 264! Used for comparison with H.264 codecs as well tuned codec from previous generation MPEG-4 ASP)
- 2005 (Dec.): DivX 6.0 (MPEG-4 ASP reference), ArcSoft H.264, Ateme H.264, ATI H.264, Elecard H.264, Fraunhofer IIS H.264, VSS H.264, x264
- 2006: DivX 6.2.5 (MPEG-4 ASP reference), MainConcept H.264, Intel H.264, VSS H.264, x264, Apple H.264, (partially), Sorenson H.264 (partially)
- 2007: XviD (MPEG-4 ASP codec), MainConcept H.264, Intel H.264, x264, AMD H.264, Artemis H.264
- 2009: XviD (MPEG-4 ASP codec), Dicas H.264, Elecard H.264, Intel IPP H.264, MainConcept H.264, x264
- 2010: XviD (MPEG-4 ASP codec), DivX H.264, Elecard H.264, Intel MediaSDK AVC/H.264, MainConcept H.264, Microsoft Expression, Encoder, Theora, x264
Detailed objective comparisons Series of Lossless Video Codecs Comparison Two size and time comparisons of lossless codecs (with lossless checking)
- 2004 Oct.
- 2007 Mar.
- 2004 (14 codecs): Alpary v2.0, AVIzlib v2.2.3, CamStudio GZIP v1.0, CorePNG v0.8.2, FFV1 ffdshow 08/08/04, GLZW v1.01, HuffYUV v2.1.1, Lagarith v188.8.131.52, LEAD JPEG v184.108.40.206, LOCO v0.2, MindVid v1.0 beta 1, MSUlab beta v0.2.4, MSUlab v0.5.2, PicVideo JPEG v.220.127.116.11, VBLE beta
- 2007 (16 codecs): Alpary, ArithYuv, AVIzlib, CamStudio GZIP, CorePNG, FastCodec, FFV1, Huffyuv, Lagarith, LOCO, LZO, MSU Lab, PICVideo, Snow, x264, YULS
in 2007 — more detailed report with new codecs including first standard H.264 (x264) MSU MPEG-4 codecs comparison Objective comparison of MPEG-4 codecs
- 2005 Mar.
DivX 5.2.1, DivX 4.12, DivX 3.22, MS MPEG-4 3688 v3, XviD 1.0.3, 3ivx D4 4.5.1, OpenDivX 0.3 Different versions of DivX was also compared. The Xvid results may be erroneous, as deblocking was disabled for it while used for DivX. Subjective Comparison of Modern Video Codecs Scientifically accurate subjective comparison using 50 experts and SAMVIQ methodology
- 2006 Feb.
DivX 6.0, Xvid 1.1.0, x264, WMV 9.0 (2 bitrates for every codec) PSNR via VQM via SSIM comparison was also done MPEG-2 Video Decoders Comparison Objective MPEG-2 Decoders comparison
- 2006 May.
bitcontrol MPEG-2 Video Decoder, DScaler MPEG2 Video Decoder, Elecard MPEG-2 Video Decoder, ffdshow MPEG-4 Video Decoder (libavcodec), InterVideo Video Decoder, Ligos MPEG Video Decoder, MainConcept MPEG Video Decoder, Pinnacle MPEG-2 Decoder Objectly tested (100 times per stream) decoders "crash test" (test on damaged stream — like scratched DVD or satellite samples) Codecs comparison Personal subjective opinion
- 2003 Nov.
3ivx, Avid AVI 2.02, Cinepak, DivX 3.11, DivX 4.12, DivX 5.0.2, DV, Huffyuv, Indeo 3.2, Indeo 4.4, Indeo 5.10, Microsoft MPEG-4 v1, Microsoft MPEG-4 v2, Microsoft RLE, Microsoft Video 1, XviD, 3ivx, Animation, Blackmagic 10-bit, Blackmagic 8-bit, Cinepak, DV, H.261, H.263, Motion-JPEG, MPEG-4 Video, PNG, Sorenson Video, Sorenson Video 3 Sometimes comparison is short (up to one text line per codec) Evaluation of Dirac and Theora Scientific paper
- 2009 Mar.
Dirac, Dirac Pro, Theora I, H.264, Motion JPEG2000 (the tested codecs are from Q2-2008) Quite detailed comparison of software available in Q2-2008; However, a buggy version of ffmpeg2Theora was used VP8 versus x264 Objective and subjective quality comparison of VP8 and x264
- 2010 Jun.
VP8, x264 VQM, SSIM and PSNR for 19 CIF video clips with bit-rates of 100, 200, 500 and 1000 kbit/s
- Comparison of media players
- List of video players (software)
- List of codecs
- Open source codecs and containers
- Comparison of audio codecs
- Comparison of container formats
- Comparison of video encoders
- Comparison of video editing software
Notes and references
- ^ Thomos, N., Boulgouris, N. V., & Strintzis, M. G. (2006, January). Optimized Transmission of JPEG2000 Streams Over Wireless Channels. IEEE Transactions on Image Processing , 15 (1).
- ^ Xiangjun, L., & Jianfei, C. ROBUST TRANSMISSION OF JPEG2000 ENCODED IMAGES OVER PACKET LOSS CHANNELS. ICME 2007 (pp. 947–950). School of Computer Engineering, Nanyang Technological University.
- ^ Xiph.Org Foundation (2009) Theora development website - news, Retrieved 2009-10-06
- ^ a b Theora.org FAQ: what is the license for Theora?
- ^ a b Dirac Video Compression, Retrieved on 2009-08-08
- ^ x264 - Jarod's unofficial builds for Windows, Retrieved on 2010-11-25
- ^ x264 - a free h264/avc encoder, Retrieved on 2011-07-10
- ^ Xvid.org, Retrieved on 2011-05-18
- ^ FFmpeg.org, Retrieved on 2009-08-09
- ^ FFavs, Retrieved on 2009-08-08
- ^ "DivX, Inc.". DivX, Inc.. http://www.divx.com/. Retrieved 19 May 2011.
- ^ VirtualDub VirtualDub documentation: codecs, Retrieved on 2009-08-08
- ^ FOURCC.org Video Codecs - Compressed Formats, Retrieved on 2009-08-08
- ^ Tom's Hardware (2001-10-22) A Tough Choice: DivX 3.20a Codec Still Better Than DivX 4.01 Codec, Retrieved on 2009-08-08
- ^ 3ivx, Retrieved on 2009-08-09
- ^ Nero AG What is Nero Digital, Retrieved on 2009-08-08
- ^ Custom Technology Corporation CINEMA CRAFT - Download, Retrieved on 2009-08-11
- ^ Pegasys Inc. What Is New, Retrieved on 2009-08-11
- ^ Compression Technologies, Inc., current maintainer of Cinepak
- ^ RealNetworks Products - Codecs, Retrieved on 2009-08-07
- ^ Huffyuv v2.1.1, Retrieved on 2009-08-09
- ^ Lagarith Lossless Video Codec, Retrieved on 2009-08-09
- ^ 
- ^ 
- ^ 
- ^ 
- ^ 
- ^ Theora.org FAQ: isn't VP3 a patented technology?
- ^ Technical description of the Cinepak codec
- ^ a b Frame rate, resolution, etc. are coded as variable length data.
- ^ a b PDF (827 KB)
- ^ Requires about 3 terabytes per uncompressed frame at maximum resolution (pg 37, Theora I Specification. March 7, 2006)
- MSU Subjective Comparison of Modern Video Codecs
- ITS - Video Quality Research
- Evaluation of Subjective Video Quality of Mobile Devices
Data compression software implementations Archivers
Lossless data compression* Audio compression
See also: compression methods and compression formats
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