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59-577: In 2003, Microsoft drafted a video compression specification based on its WMV 9 format and submitted it to SMPTE for standardization. The standard was officially approved in March 2006 as SMPTE 421M, better known as VC-1 , thus making the WMV 9 format an open standard. VC-1 became one of the three video formats for the Blu-ray video disc, along with H.262/MPEG-2 Part 2 and H.264/MPEG-4 AVC . A WMV file uses

118-496: A video coding specification . Some such specifications are written and approved by standardization organizations as technical standards , and are thus known as a video coding standard . There are de facto standards and formal standards. Video content encoded using a particular video coding format is normally bundled with an audio stream (encoded using an audio coding format ) inside a multimedia container format such as AVI , MP4 , FLV , RealMedia , or Matroska . As such,

177-701: A DVD player will first have to convert to MPEG-2 before burning a DVD (average file sizes in MPEG-2 are 5 to 6 times the .wmv file). The audio format used in conjunction with Windows Media Video is typically some version of Windows Media Audio , or in rarer cases, the deprecated Sipro ACELP.net audio format. Microsoft recommends that ASF files containing non-Windows Media formats use the generic .ASF file extension. Software that can play WMV files includes Windows Media Player , RealPlayer , MPlayer , Media Player Classic , VLC Media Player and K-Multimedia Player . The Microsoft Zune media management software supports

236-580: A custom block cipher, RC4 stream cipher and the SHA-1 hashing function. Although WMV is generally packed into the ASF container format, it can also be put into the Matroska container format (with file extension .mkv ), or AVI container format (extension .avi ). One common way to store WMV in an AVI file is to use the WMV 9 Video Compression Manager (VCM) codec implementation. Windows Media Video (WMV)

295-444: A data file or bitstream . It typically uses a standardized video compression algorithm, most commonly based on discrete cosine transform (DCT) coding and motion compensation . A specific software, firmware , or hardware implementation capable of compression or decompression in a specific video coding format is called a video codec . Some video coding formats are documented by a detailed technical specification document known as

354-518: A few examples are Windows Movie Maker , Windows Media Encoder , Microsoft Expression Encoder , Sorenson Squeeze , Sony Vegas Pro , AVS Video Editor , VSDC Free Video Editor , Telestream Episode , Telestream FlipFactory , and FFmpeg . Programs that encode using the WMV Image format include Windows Media Encoder , AVS Video Editor , and Photo Story . While none of the WMV formats themselves contain any digital rights management facilities,

413-428: A free-as-in-beer video codec, the press release refers to the H.264 video coding format as a codec ("choice of a common video codec"), but calls Cisco's implementation of a H.264 encoder/decoder a codec shortly thereafter ("open-source our H.264 codec"). A video coding format does not dictate all algorithms used by a codec implementing the format. For example, a large part of how video compression typically works

472-416: A lot more computing power than editing intraframe compressed video with the same picture quality. But, this compression is not very effective to use for any audio format. A video coding format can define optional restrictions to encoded video, called profiles and levels. It is possible to have a decoder which only supports decoding a subset of profiles and levels of a given video format, for example to make

531-556: A much more efficient form of compression for video coding. The CCITT received 14 proposals for DCT-based video compression formats, in contrast to a single proposal based on vector quantization (VQ) compression. The H.261 standard was developed based on motion-compensated DCT compression. H.261 was the first practical video coding standard, and uses patents licensed from a number of companies, including Hitachi , PictureTel , NTT , BT , and Toshiba , among others. Since H.261, motion-compensated DCT compression has been adopted by all

590-586: A new WMV format called Windows Media Video 9 Advanced Profile . It improves compression efficiency for interlaced content and is made transport-independent, making it able to be encapsulated in an MPEG transport stream or RTP packet format. The format is not compatible with previous WMV 9 formats, however. WMV is a mandatory video format for PlaysForSure -certified online stores and devices, as well as Portable Media Center devices. The Microsoft Zune , Xbox 360 , Windows Mobile -powered devices with Windows Media Player, as well as many uncertified devices, support

649-407: A number of companies, primarily Mitsubishi, Hitachi and Panasonic . The most widely used video coding format as of 2019 is H.264/MPEG-4 AVC . It was developed in 2003, and uses patents licensed from a number of organizations, primarily Panasonic, Godo Kaisha IP Bridge and LG Electronics . In contrast to the standard DCT used by its predecessors, AVC uses the integer DCT . H.264 is one of

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708-499: A patent lawsuit due to submarine patents . The motivation behind many recently designed video coding formats such as Theora , VP8 , and VP9 have been to create a ( libre ) video coding standard covered only by royalty-free patents. Patent status has also been a major point of contention for the choice of which video formats the mainstream web browsers will support inside the HTML video tag. The current-generation video coding format

767-412: A screencast helps software developers show off their work. Educators may also use screencasts as another means of integrating technology into the curriculum. Students can record video and audio as they demonstrate the proper procedure to solve a problem on an interactive whiteboard. Screencasts are useful tools for ordinary software users as well: They help filing report bugs in which the screencasts take

826-499: A single picture of a computer screen, a screencast is essentially a movie of the changes over time that a user sees on a computer screen, that can be enhanced with audio narration and captions. In 2004, columnist Jon Udell invited readers of his blog to propose names for the emerging genre. Udell selected the term "screencast", which was proposed by both Joseph McDonald and Deeje Cooley. The terms "screencast," " screencam " and "screen recording" are often used interchangeably, due to

885-413: A visual explanation of the content presented. Open-source tools exist for both screencasting and livestreaming the recorded video. Trial versions of screencasting programs often apply a watermark , encouraging users to purchase the full version in order to remove it. An alternative solution for capturing a screencast is the use of a hardware RGB or DVI frame grabber card. This approach places

944-454: Is HEVC (H.265), introduced in 2013. AVC uses the integer DCT with 4x4 and 8x8 block sizes, and HEVC uses integer DCT and DST transforms with varied block sizes between 4x4 and 32x32. HEVC is heavily patented, mostly by Samsung Electronics , GE , NTT , and JVCKenwood . It is challenged by the AV1 format, intended for free license. As of 2019 , AVC is by far the most commonly used format for

1003-421: Is a clear conceptual difference between a specification and its implementations. Video coding formats are described in specifications, and software, firmware , or hardware to encode/decode data in a given video coding format from/to uncompressed video are implementations of those specifications. As an analogy, the video coding format H.264 (specification) is to the codec OpenH264 (specific implementation) what

1062-412: Is a form of lossless video used in some circumstances such as when sending video to a display over a HDMI connection. Some high-end cameras can also capture video directly in this format. Interframe compression complicates editing of an encoded video sequence. One subclass of relatively simple video coding formats are the intra-frame video formats, such as DV , in which each frame of the video stream

1121-450: Is a hybrid coding algorithm, which combines two key data compression techniques: discrete cosine transform (DCT) coding in the spatial dimension , and predictive motion compensation in the temporal dimension . DCT coding is a lossy block compression transform coding technique that was first proposed by Nasir Ahmed , who initially intended it for image compression , while he was working at Kansas State University in 1972. It

1180-575: Is a video slideshow format. The format works by applying timing, panning and transition effects to a series of images during playback. The codec achieves a higher compression ratio and image quality than WMV 9 for still images as files encoded with WMV Image store static images rather than full-motion video. Since the format relies on the decoder (player) to generate video frames in real-time, playing WMV Image files even at moderate resolutions (e.g. 30 frames per second at 1024 px × 768 px resolution) requires heavy computer processing. The latest version of

1239-451: Is by finding similarities between video frames (block-matching) and then achieving compression by copying previously-coded similar subimages (such as macroblocks ) and adding small differences when necessary. Finding optimal combinations of such predictors and differences is an NP-hard problem, meaning that it is practically impossible to find an optimal solution. Though the video coding format must support such compression across frames in

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1298-518: Is compressed independently without referring to other frames in the stream, and no attempt is made to take advantage of correlations between successive pictures over time for better compression. One example is Motion JPEG , which is simply a sequence of individually JPEG -compressed images. This approach is quick and simple, at the expense of the encoded video being much larger than a video coding format supporting Inter frame coding. Because interframe compression copies data from one frame to another, if

1357-547: Is that, with intraframe systems, each frame uses a similar amount of data. In most interframe systems, certain frames (such as I-frames in MPEG-2 ) are not allowed to copy data from other frames, so they require much more data than other frames nearby. It is possible to build a computer-based video editor that spots problems caused when I frames are edited out while other frames need them. This has allowed newer formats like HDV to be used for editing. However, this process demands

1416-509: Is the most recognized video compression format within the WMV family. Usage of the term WMV often refers to the Microsoft Windows Media Video format only. Its main competitors are MPEG-4 AVC , AVS , RealVideo , and MPEG-4 ASP . The first version of the format, WMV 7, was introduced in 1999, and was built upon Microsoft's implementation of MPEG-4 Part 2 . Continued proprietary development led to newer versions of

1475-531: The Advanced Systems Format (ASF) container format to encapsulate the encoded multimedia content. While the ASF can encapsulate multimedia in other encodings than those the WMV file standard specifies, those ASF files should use the .asf file extension and not the .wmv file extension. The ASF container can optionally support digital rights management using a combination of elliptic curve cryptography key exchange, DES block cipher,

1534-478: The C Programming Language (specification) is to the compiler GCC (specific implementation). Note that for each specification (e.g., H.264 ), there can be many codecs implementing that specification (e.g., x264 , OpenH264, H.264/MPEG-4 AVC products and implementations ). This distinction is not consistently reflected terminologically in the literature. The H.264 specification calls H.261 , H.262 , H.263 , and H.264 video coding standards and does not contain

1593-432: The main and high profiles but not in baseline . A level is a restriction on parameters such as maximum resolution and data rates. Screencast A screencast is a digital recording of computer screen output, also known as a video screen capture or a screen recording , often containing audio narration . The term screencast compares with the related term screenshot ; whereas screenshot generates

1652-461: The 3rd party Flip4Mac , a QuickTime Component developed by Telestream that allowed Macintosh users to play WMV files in any player that used the QuickTime framework. Telestream ended sales of Flip4Mac on 1 July 2019 and officially ended support on 28 June 2020. The Elmedia player, which can play WMV files on Macintosh computers, is still available. Many programs can export video in WMV format;

1711-466: The ASF container format, in which a WMV stream may be encapsulated, can. Windows Media DRM, which can be used in conjunction with WMV, supports time-limited subscription video services such as those offered by CinemaNow . Windows Media DRM, a component of PlaysForSure and Windows Media Connect , is supported on many modern portable video devices and streaming media clients such as the Xbox 360. WMV has been

1770-521: The DCT, Hadamard transform , Fourier transform , slant transform, and Karhunen-Loeve transform . However, his algorithm was initially limited to intra-frame coding in the spatial dimension. In 1975, John A. Roese and Guner S. Robinson extended Habibi's hybrid coding algorithm to the temporal dimension, using transform coding in the spatial dimension and predictive coding in the temporal dimension, developing inter-frame motion-compensated hybrid coding. For

1829-569: The WMV format, but uses a Zune-specific variation of Windows Media DRM which is used by PlaysForSure. Many third-party players exist for various platforms such as Linux that use the FFmpeg implementation of the WMV format. On the Macintosh platform, Microsoft released a PowerPC version of Windows Media Player for Mac OS X in 2003, but further development of the software ceased. From January 2006 to May 2014, Microsoft endorsed and distributed

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1888-459: The bitstream format, by not needlessly mandating specific algorithms for finding such block-matches and other encoding steps, the codecs implementing the video coding specification have some freedom to optimize and innovate in their choice of algorithms. For example, section 0.5 of the H.264 specification says that encoding algorithms are not part of the specification. Free choice of algorithm also allows different space–time complexity trade-offs for

1947-414: The decoder program/hardware smaller, simpler, or faster. A profile restricts which encoding techniques are allowed. For example, the H.264 format includes the profiles baseline , main and high (and others). While P-slices (which can be predicted based on preceding slices) are supported in all profiles, B-slices (which can be predicted based on both preceding and following slices) are supported in

2006-610: The desktop. In classrooms, teachers and students can use this tool to create videos to explain content, vocabulary, etc. Videos can make class time more productive for both teachers and students. Screencasts may increase student engagement and achievement and also provide more time in which students can work collaboratively in groups, so screencasts help them to think through cooperative learning. In addition, screencasts allow students to move at their own pace since they can pause or review content anytime and anywhere. Screencasts are excellent for those learners who just need an oral as well as

2065-583: The file type WebM , which specifies the container format (Matroska), but also exactly which video ( VP8 ) and audio ( Vorbis ) compression format is inside the Matroska container, even though Matroska is capable of containing VP9 video, and Opus audio support was later added to the WebM specification. A format is the layout plan for data produced or consumed by a codec . Although video coding formats such as H.264 are sometimes referred to as codecs , there

2124-438: The format, WMV 9.1 Image, used by Photo Story 3, features additional transformation effects, but is not compatible with the original WMV 9 Image format. Hardware support for WMV Image is available from Portable Media Centers, Windows Mobile -powered devices with Windows Media Player 10 Mobile. Since no known domestic DVD player supports this format, users of Photo Story 3 wishing to generate material capable of being played in

2183-431: The format, but the bit stream syntax was not frozen until WMV 9. While all versions of WMV support variable bit rate , average bit rate , and constant bit rate , WMV 9 introduced several important features including native support for interlaced video , non-square pixels , and frame interpolation . WMV 9 also introduced a new profile titled Windows Media Video 9 Professional , which is activated automatically whenever

2242-590: The format. WMV HD mandates the use of WMV 9 for its certification program, at quality levels specified by Microsoft. WMV used to be the only supported video format for the Microsoft Silverlight platform, but the H.264 format is now also supported starting with version 3. Windows Media Video Screen (WMV Screen) are video formats that specialise in screencast content. They can capture live screen content, or convert video from third-party screen-capture programs into WMV 9 Screen files. They work best when

2301-501: The major video coding standards (including the H.26x and MPEG formats) that followed. MPEG-1 , developed by the Moving Picture Experts Group (MPEG), followed in 1991, and it was designed to compress VHS -quality video. It was succeeded in 1994 by MPEG-2 / H.262 , which was developed with patents licensed from a number of companies, primarily Sony , Thomson and Mitsubishi Electric . MPEG-2 became

2360-469: The market influence of ScreenCam as a screencasting product of the early 1990s. ScreenCam, however, is a federal trademark in the United States , whereas screencast is not trademarked and has established use in publications as part of Internet and computing vernacular. Screen recording is now the most generic term. Screencasts can help demonstrate and teach the use of software features. Creating

2419-406: The organizers and makes the knowledge available to a broader audience. This strategy of recording seminars is already widely used in fields where using a simple video camera or audio recorder is insufficient to make a useful recording of a seminar. Computer-related seminars need high quality and easily readable recordings of screen contents which is usually not achieved by a video camera that records

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2478-457: The original frame is simply cut out (or lost in transmission), the following frames cannot be reconstructed properly. Making cuts in intraframe-compressed video while video editing is almost as easy as editing uncompressed video: one finds the beginning and ending of each frame, and simply copies bit-for-bit each frame that one wants to keep, and discards the frames one does not want. Another difference between intraframe and interframe compression

2537-459: The place of potentially unclear written explanations; they help showing others how a given task is accomplished in a specific software environment. Organizers of seminars may choose to routinely record complete seminars and make them available to all attendees for future reference and/or sell these recordings to people who cannot afford the fee of the live seminar or do not have the time to attend it. This will generate an additional revenue stream for

2596-514: The recording, compression, and distribution of video content, used by 91% of video developers, followed by HEVC which is used by 43% of developers. Consumer video is generally compressed using lossy video codecs , since that results in significantly smaller files than lossless compression. Some video coding formats designed explicitly for either lossy or lossless compression, and some video coding formats such as Dirac and H.264 support both. Uncompressed video formats, such as Clean HDMI ,

2655-588: The same video coding format, so a live feed can use a fast but space-inefficient algorithm, and a one-time DVD encoding for later mass production can trade long encoding-time for space-efficient encoding. The concept of analog video compression dates back to 1929, when R.D. Kell in Britain proposed the concept of transmitting only the portions of the scene that changed from frame-to-frame. The concept of digital video compression dates back to 1952, when Bell Labs researchers B.M. Oliver and C.W. Harrison proposed

2714-546: The source material is mainly static and contains a small color palette . One of the uses for the format is computer step-by-step demonstration videos. The first version of the format was WMV 7 Screen. The second version, WMV 9 Screen, supports VBR encoding in addition to CBR. Additionally there is MSA1 (aka “MS ATC Screen codec” or “MSS3”) which is used in Live Meeting 2007. FourCCs for the formats are MSS1 , MSS2 and MSA1 . Windows Media Video Image (WMV Image)

2773-449: The spatial transform coding, they experimented with different transforms, including the DCT and the fast Fourier transform (FFT), developing inter-frame hybrid coders for them, and found that the DCT is the most efficient due to its reduced complexity, capable of compressing image data down to 0.25- bit per pixel for a videotelephone scene with image quality comparable to a typical intra-frame coder requiring 2-bit per pixel. The DCT

2832-532: The standard coding technique for video compression from the late 1980s onwards. The first digital video coding standard was H.120 , developed by the CCITT (now ITU-T) in 1984. H.120 was not usable in practice, as its performance was too poor. H.120 used motion-compensated DPCM coding, a lossless compression algorithm that was inefficient for video coding. During the late 1980s, a number of companies began experimenting with discrete cosine transform (DCT) coding,

2891-434: The standard video format for DVD and SD digital television . Its motion-compensated DCT algorithm was able to achieve a compression ratio of up to 100:1, enabling the development of digital media technologies such as video on demand (VOD) and high-definition television (HDTV). In 1999, it was followed by MPEG-4 / H.263 , which was a major leap forward for video compression technology. It uses patents licensed from

2950-542: The subject of numerous complaints from users and the press. Users dislike the digital rights management system which is sometimes attached to WMV files. In 2007, the loss of the ability to restore licenses for WMV files in the Windows Media Player 11 was not positively received. Video compression specification A video coding format (or sometimes video compression format ) is a content representation format of digital video content, such as in

3009-443: The transmission bandwidth of analog television signals. The earliest digital video coding algorithms were either for uncompressed video or used lossless compression , both methods inefficient and impractical for digital video coding. Digital video was introduced in the 1970s, initially using uncompressed pulse-code modulation (PCM), requiring high bitrates around 45–200 Mbit/s for standard-definition (SD) video, which

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3068-431: The use of differential pulse-code modulation (DPCM) in video coding. In 1959, the concept of inter-frame motion compensation was proposed by NHK researchers Y. Taki, M. Hatori and S. Tanaka, who proposed predictive inter-frame video coding in the temporal dimension . In 1967, University of London researchers A.H. Robinson and C. Cherry proposed run-length encoding (RLE), a lossless compression scheme, to reduce

3127-460: The user normally does not have a H.264 file, but instead has a video file , which is an MP4 container of H.264-encoded video, normally alongside AAC -encoded audio. Multimedia container formats can contain one of several different video coding formats; for example, the MP4 container format can contain video coding formats such as MPEG-2 Part 2 or H.264. Another example is the initial specification for

3186-640: The video encoding standards for Blu-ray Discs ; all Blu-ray Disc players must be able to decode H.264. It is also widely used by streaming internet sources, such as videos from YouTube , Netflix , Vimeo , and the iTunes Store , web software such as the Adobe Flash Player and Microsoft Silverlight , and also various HDTV broadcasts over terrestrial ( ATSC standards , ISDB-T , DVB-T or DVB-T2 ), cable ( DVB-C ), and satellite ( DVB-S2 ). A main problem for many video coding formats has been patents , making it expensive to use or potentially risking

3245-514: The video resolution exceeds 300,000 pixels (e.g., 528 px × 576 px, 640 px × 480 px or 768 px × 432 px and beyond) and the bitrate 1 Mbit/s. It is targeted towards high-definition video content, at resolutions such as 720p and 1080p . The Simple and Main profile levels in WMV 9 are compliant with the same profile levels in the VC-1 specification. The Advanced Profile in VC-1 is implemented in

3304-563: The word codec . The Alliance for Open Media clearly distinguishes between the AV1 video coding format and the accompanying codec they are developing, but calls the video coding format itself a video codec specification . The VP9 specification calls the video coding format VP9 itself a codec . As an example of conflation, Chromium's and Mozilla's pages listing their video formats support both call video coding formats, such as H.264 codecs . As another example, in Cisco's announcement of

3363-471: Was applied to video encoding by Wen-Hsiung Chen, who developed a fast DCT algorithm with C.H. Smith and S.C. Fralick in 1977, and founded Compression Labs to commercialize DCT technology. In 1979, Anil K. Jain and Jaswant R. Jain further developed motion-compensated DCT video compression. This led to Chen developing a practical video compression algorithm, called motion-compensated DCT or adaptive scene coding, in 1981. Motion-compensated DCT later became

3422-508: Was then developed into a practical image compression algorithm by Ahmed with T. Natarajan and K. R. Rao at the University of Texas in 1973, and was published in 1974. The other key development was motion-compensated hybrid coding. In 1974, Ali Habibi at the University of Southern California introduced hybrid coding, which combines predictive coding with transform coding. He examined several transform coding techniques, including

3481-488: Was up to 2,000 times greater than the telecommunication bandwidth (up to 100   kbit/s ) available until the 1990s. Similarly, uncompressed high-definition (HD) 1080p video requires bitrates exceeding 1   Gbit/s , significantly greater than the bandwidth available in the 2000s. Practical video compression emerged with the development of motion-compensated DCT (MC DCT) coding, also called block motion compensation (BMC) or DCT motion compensation. This

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