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46-501: Audio Video Interleave (also Audio Video Interleaved and known by its initials and filename extension AVI , usually pronounced / ˌ eɪ . v iː ˈ aɪ / ) is a proprietary multimedia container format and Windows standard introduced by Microsoft in November 1992 as part of its Video for Windows software. AVI files can contain both audio and video data in a file container that allows synchronous audio-with-video playback. Like

92-661: A Uniform Type Identifier by which to identify the file type internally. The use of a filename extension in a command name appears occasionally, usually as a side effect of the command having been implemented as a script, e.g., for the Bourne shell or for Python , and the interpreter name being suffixed to the command name, a practice common on systems that rely on associations between filename extension and interpreter, but sharply deprecated in Unix-like systems, such as Linux , Oracle Solaris , BSD -based systems, and Apple's macOS , where

138-503: A file with its media type as an extended attribute. Some desktop environments , such as KDE Plasma and GNOME , associate a media type with a file by examining both the filename suffix and the contents of the file, in the fashion of the file command, as a heuristic . They choose the application to launch when a file is opened based on that media type, reducing the dependency on filename extensions. macOS uses both filename extensions and media types, as well as file type codes , to select

184-453: A file's data into blocks, or "chunks". Each chunk is identified by a FourCC tag. An AVI file takes the form of a RIFF header, which is then divided into two mandatory chunks and one optional chunk. The first chunk is identified by the "hdrl" tag, which stores the information required by the codec to decompress the AVI file for viewing. The second sub-chunk is identified by the "movi" tag, containing

230-476: A file's type to be stored in the file as an extended attribute. Microsoft's Windows NT 's native file system, NTFS , and the later ReFS , also store the file name as a single string; again, the convention of using suffixes to simulate extensions continued, for compatibility with existing versions of Windows. In Windows NT 3.5 , a variant of the FAT file system, called VFAT appeared; it supports longer file names, with

276-554: A period, and an extension of up to three letters. The FAT file system for DOS and Windows stores file names as an 8-character name and a three-character extension. The period character is not stored. The High Performance File System (HPFS), used in Microsoft and IBM 's OS/2 stores the file name as a single string, with the "." character as just another character in the file name. The convention of using suffixes continued, even though HPFS supports extended attributes for files, allowing

322-480: A program always has the same extension-less name, with only the interpreter directive and/or magic number changing, and references to the program from other programs remain valid. The default behavior of File Explorer , the file browser provided with Microsoft Windows , is for filename extensions to not be displayed. Malicious users have tried to spread computer viruses and computer worms by using file names formed like LOVE-LETTER-FOR-YOU.TXT.vbs . The hope

368-473: A single file type; there was an unambiguous mapping between extension and icon. When the Internet age first arrived, those using Windows systems that were still restricted to 8.3 filename formats had to create web pages with names ending in .HTM , while those using Macintosh or UNIX computers could use the recommended .html filename extension. This also became a problem for programmers experimenting with

414-414: A suffix — for example, executables and ordinary text files usually have no suffixes in their names. File systems for UNIX-like operating systems also store the file name as a single string, with "." as just another character in the file name. A file with more than one suffix is sometimes said to have more than one extension, although terminology varies in this regard, and most authors define extension in

460-752: A variety of ways, filename extensions started to become closely associated with certain products—even specific product versions. For example, early WordStar files used .WS or .WS n , where n was the program's version number. Also, conflicting uses of some filename extensions developed. One example is .rpm , used for both RPM Package Manager packages and RealPlayer Media files;. Others are .qif , shared by DESQview fonts, Quicken financial ledgers, and QuickTime pictures; .gba , shared by GrabIt scripts and Game Boy Advance ROM images; .sb , used for SmallBasic and Scratch ; and .dts , being used for Dynamix Three Space and DTS . In many Internet protocols, such as HTTP and MIME email ,

506-517: A way that does not allow more than one in the same file name. More than one extension usually represents nested transformations, such as files.tar.gz (the .tar indicates that the file is a tar archive of one or more files, and the .gz indicates that the tar archive file is compressed with gzip ). Programs transforming or creating files may add the appropriate extension to names inferred from input file names (unless explicitly given an output file name), but programs reading files usually ignore

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552-432: Is a time-consuming process. Many FireWire controllers only captured to one or the other type. However, almost all relevant software supports both Type 1 and Type 2 editing and rendering, including Adobe Premiere. Thus, many users are unaware of the fact that there are two types of DV AVI files. Filename extension Some file systems implement filename extensions as a feature of the file system itself and may limit

598-462: Is changed, the command name extension is changed as well, and the OS provides a consistent API by allowing the same extensionless version of the command to be used in both cases. This method suffers somewhat from the essentially global nature of the association mapping, as well as from developers' incomplete avoidance of extensions when calling programs, and that developers can not force that avoidance. Windows

644-587: Is derived from matryoshka ( Russian : матрёшка [mɐˈtrʲɵʂkə] ), the Russian word for the hollow wooden dolls which open to expose another smaller doll, that in turn opens to expose another doll, and so on. The logo writes it as "Matroška"; the letter š , an "s" with a caron over it, represents the "sh" sound ( / ʂ / ) in various languages. The use of EBML allows extension for future format changes. The Matroska team has expressed some of their long-term goals on Doom9.org and Hydrogenaudio forums. Thus,

690-433: Is freely available to both create and correctly replay AVI files which use the techniques described here. DV AVI is a type of AVI file where the video has been compressed to conform with DV standards. There are two types of DV-AVI files: Type 1 is actually the newer of the two types. Microsoft made the "type" designations, and decided to name their older VfW-compatible version "Type 2", which only furthered confusion about

736-476: Is just a marker and the content of the file does not have to match it. This can be used to disguise malicious content. When trying to identify a file for security reasons, it is therefore considered dangerous to rely on the extension alone and a proper analysis of the content of the file is preferred. For example, on UNIX-like systems, it is not uncommon to find files with no extensions at all, as commands such as file are meant to be used instead, and will read

782-636: Is that this will appear as LOVE-LETTER-FOR-YOU.TXT , a harmless text file, without alerting the user to the fact that it is a harmful computer program, in this case, written in VBScript . Default behavior for ReactOS is to display filename extensions in ReactOS Explorer . Later Windows versions (starting with Windows XP Service Pack 2 and Windows Server 2003 ) included customizable lists of filename extensions that should be considered "dangerous" in certain "zones" of operation, such as when downloaded from

828-400: Is the only remaining widespread employer of this mechanism. On systems with interpreter directives , including virtually all versions of Unix, command name extensions have no special significance, and are by standard practice not used, since the primary method to set interpreters for scripts is to start them with a single line specifying the interpreter to use. In these environments, including

874-595: The DVD video format , AVI files support multiple streaming audio and video, although these features are seldom used. Many AVI files use the file format extensions developed by the Matrox OpenDML group in February 1996. These files are supported by Microsoft, and are unofficially called " AVI 2.0 ". In 2010 the US government 's National Archives and Records Administration defined AVI as

920-465: The Java programming language , since it requires the four-letter suffix .java for source code files and the five-letter suffix .class for Java compiler object code output files. Filename extensions may be considered a type of metadata . They are commonly used to imply information about the way data might be stored in the file. The exact definition, giving the criteria for deciding what part of

966-416: The web or received as an e-mail attachment. Modern antivirus software systems also help to defend users against such attempted attacks where possible. Some viruses take advantage of the similarity between the " .com " top-level domain and the ".COM" filename extension by emailing malicious, executable command-file attachments under names superficially similar to URLs ( e.g. , "myparty.yahoo.com"), with

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1012-405: The (compressed) data format used inside the chunk. An AVI file may carry audio and visual data inside the chunks in virtually any compression scheme, including Full Frame (Uncompressed), Indeo , run-length encoding , and Microsoft Video 1 . Some programs, like VLC , complain when the "idx1" index sub-chunk is not found, as it is required for efficient moving among timestamps. They offer to "fix"

1058-478: The Internet. For instance, a content author may specify the extension svgz for a compressed Scalable Vector Graphics file, but a web server that does not recognize this extension may not send the proper content type application/svg+xml and its required compression header, leaving web browsers unable to correctly interpret and display the image. BeOS , whose BFS file system supports extended attributes, would tag

1104-487: The actual audio and visual data that make up the AVI video. The third optional chunk is identified by the "idx1" tag, which indexes the offsets of the data chunks within the file. By way of the RIFF format, the audio and visual data contained in the "movi" chunk can be encoded or decoded by software called a codec , which is an abbreviation for (en)coder/decoder. Upon creation of the file, the codec translates between raw data and

1150-415: The advent of graphical user interfaces , the issue of file management and interface behavior arose. Microsoft Windows allowed multiple applications to be associated with a given extension, and different actions were available for selecting the required application, such as a context menu offering a choice between viewing, editing or printing the file. The assumption was still that any extension represented

1196-527: The chunk. As such, it is theoretically possible to expand any RIFF file format, including AVI, to support almost any conceivable metadata. Some of the limitations of AVI in modern use relate to a lack of standardization in this metadata (see Limitations below). Since its introduction in the early 90s, new computer video techniques have been introduced which the original AVI specification did not anticipate. More recent container formats (such as Matroska , Ogg and MP4 ) solve all these problems, although software

1242-667: The community quickly migrated to the new project. In 2010, it was announced that the WebM audio/video format would be based on a profile of the Matroska container format together with VP8 video and Vorbis audio. On 31 October 2014, Microsoft confirmed that Windows 10 would support HEVC and Matroska out of the box , according to a statement from Gabriel Aul, the leader of Microsoft Operating Systems Group's Data and Fundamentals Team. Windows 10 Technical Preview Build 9860 added platform level support for HEVC and Matroska. "Matroska"

1288-404: The effect that unaware users click on email-embedded links that they think lead to websites but actually download and execute the malicious attachments. There have been instances of malware crafted to exploit vulnerabilities in some Windows applications which could cause a stack-based buffer overflow when opening a file with an overly long, unhandled filename extension. The filename extension

1334-450: The extension in a command name unnecessarily exposes an implementation detail which puts all references to the commands from other programs at future risk if the implementation changes. For example, it would be perfectly normal for a shell script to be reimplemented in Python or Ruby, and later in C or C++, all of which would change the name of the command were extensions used. Without extensions,

1380-411: The extension is a separate namespace from the filename. Under Microsoft's DOS and Windows , extensions such as EXE , COM or BAT indicate that a file is a program executable . In OS/360 and successors , the part of the dataset name following the last period, called the low level qualifier, is treated as an extension by some software, e.g., TSO EDIT, but it has no special significance to

1426-558: The file by building an index temporarily or permanently. As a derivative of the Resource Interchange File Format (RIFF), AVI files are commonly tagged with metadata in the INFO chunk. In addition, AVI files can embed Extensible Metadata Platform . By design, any RIFF file can legally include additional chunks of data, each identified by a four-character code; software which does not understand that particular code should skip

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1472-443: The file name being treated as a single string. Windows 95 , with VFAT, introduced support for long file names, and removed the 8.3 name/extension split in file names from non-NT Windows. The classic Mac OS disposed of filename-based extension metadata entirely; it used, instead, a distinct file type code to identify the file format. Additionally, a creator code was specified to determine which application would be launched when

1518-499: The file name is its extension, belongs to the rules of the specific file system used; usually the extension is the substring which follows the last occurrence, if any, of the dot character ( example: txt is the extension of the filename readme.txt , and html the extension of index.html ). On file systems of some mainframe systems such as CMS in VM , VMS , and of PC systems such as CP/M and derivative systems such as MS-DOS ,

1564-473: The file's icon was double-clicked . macOS , however, uses filename suffixes as a consequence of being derived from the UNIX-like NeXTSTEP operating system, in addition to using type and creator codes. In Commodore systems, files can only have four extensions: PRG, SEQ, USR, REL. However, these are used to separate data types used by a program and are irrelevant for identifying their contents. With

1610-600: The file's header to determine its content. Matroska Matroska is a project to create a container format that can hold an unlimited number of video, audio, picture, or subtitle tracks in one file. The Matroska Multimedia Container is similar in concept to other containers like AVI , MP4 , or Advanced Systems Format (ASF), but is an open standard . Matroska file extensions are .mkv for video (which may include subtitles or audio), .mk3d for stereoscopic video, .mka for audio-only files (which may include subtitles), and .mks for subtitles only. The project

1656-457: The following are "goals", not necessarily existing features, of Matroska: Matroska is supported by a non-profit organization ( association loi 1901 ) in France, and the specifications are open to everyone. It is a royalty-free open standard that is free to use, and its technical specifications are available for private and commercial use. The Matroska development team licenses its libraries under

1702-413: The information; it is mostly intended for the human user. It is more common, especially in binary files, for the file to contain internal or external metadata describing its contents. This model generally requires the full filename to be provided in commands, whereas the metadata approach often allows the extension to be omitted. In DOS and 16-bit Windows , file names have a maximum of 8 characters,

1748-420: The interpreter is normally specified as a header in the script (" shebang "). On association-based systems, the filename extension is generally mapped to a single, system-wide selection of interpreter for that extension (such as ".py" meaning to use Python), and the command itself is runnable from the command line even if the extension is omitted (assuming appropriate setup is done). If the implementation language

1794-596: The length and format of the extension, while others treat filename extensions as part of the filename without special distinction. The Multics file system stores the file name as a single string, not split into base name and extension components, allowing the "." to be just another character allowed in file names. It allows for variable-length filenames, permitting more than one dot, and hence multiple suffixes, as well as no dot, and hence no suffix. Some components of Multics, and applications running on it, use suffixes to indicate file types, but not all files are required to have

1840-428: The official wrapper for preserving digital video . Publishers faced a predicament regarding how they should distribute videos on CD-ROMs . Thirty seconds of video displayed in 24-bit color and at thirty frames per second and Super VGA resolutions could take up 680 megabytes of space—the storage capacity of most CD-ROMs in 1992. Lossily compressing the videos would save a lot of space, but not without degrading

1886-515: The operating system itself; the same applies to Unix files in MVS. The filename extension was originally used to determine the file's generic type. The need to condense a file's type into three characters frequently led to abbreviated extensions. Examples include using .GFX for graphics files, .TXT for plain text , and .MUS for music. However, because many different software programs have been made that all handle these data types (and others) in

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1932-404: The quality of the videos. Publishers who were more concerned about video quality instead were searching for an ideal compression algorithm that would compress the video files while still preserving the quality. Microsoft recognized the problem and sought to develop a standard that would losslessly compress the video files. They also recognized that because of the hardware requirements for playing

1978-451: The two types. In the late 1990s through early 2000s, most professional-level DV software, including non-linear editing programs, only supported Type 1. One notable exception was Adobe Premiere , which only supported Type 2. High-end FireWire controllers usually captured to Type 1 only, while "consumer" level controllers usually captured to Type 2 only. Software is and was available for converting Type 1 AVIs to Type 2, and vice versa, but this

2024-413: The type of a bitstream is stated as the media type , or MIME type, of the stream, rather than a filename extension. This is given in a line of text preceding the stream, such as Content-type: text/plain . There is no standard mapping between filename extensions and media types, resulting in possible mismatches in interpretation between authors, web servers, and client software when transferring files over

2070-486: The videos in uncompressed quality, which at the time were demanding, it needed to allow users of low-end computers to play the videos in compressed quality. They developed and published the Audio Video Interleave format on November 10, 1992, as part of their Video for Windows, and included support for codecs to satisfy those users. AVI is a subformat of the Resource Interchange File Format (RIFF), which divides

2116-595: Was announced on 6 December 2002 as a fork of the Multimedia Container Format (MCF), after disagreements between MCF lead developer Lasse Kärkkäinen and soon-to-be Matroska founder Steve Lhomme about the use of the Extensible Binary Meta Language (EBML) instead of a binary format. This coincided with a 6-month coding break by the MCF's lead developer for his military service, during which most of

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