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File Extension Glossary

File extensions are the suffix to the name of a computer file that indicates the encoding of its contents or usage.

You’re likely familiar with file extensions—you’ve seen them at the end of your documents, media files, and more. A file extension, or filename extension, is nothing more than the last characters after the period in the name of a file. For example: picture.jpeg or essay.doc.

But perhaps you’re not aware that learning the different types and groupings of filenames can help you understand how certain software can be used to help you convert, store, and send files.’s handy file extension glossary can help you find the file type you have, what you might need, or what other file extensions could help you achieve your goals.



AAC (Advanced Audio Coding) AAC was developed to improve upon the MP3 audio format, and uses a more advanced form of compression. The current version of the AAC codec was developed as part of the MPEG4 standard. Versions of AAC are used by Apple in their popular iTunes® Store, as well as Sony in their PlayStation®3 game consoles. Files may appear with the “.m4a” or “.mp4″ filename extension. Songs with DRM (digital rights management) purchased from the iTunes Store usually have an “.m4p” extension (with the “p” at the end to denote “protected”).

AI ( An Adobe Illustrator document.

AIFF (example.aiff) An audio format for Macintosh operating systems commonly used for storing uncompressed, CD-quality sound (similar to WAV files for Windows-based PCs). AIFF is considered a container format.

APD (example.apd) An Aldus PageMaker document.

Apple Lossless Apple Lossless Encoding (also known as Apple Lossless, Apple Lossless Audio Codec or ALE) is a lossless audio codec developed by Apple Computer to provide full, CD-quality audio in about half the space of the original file.

ATRAC™ Developed by Sony engineers in the early 90s for the MiniDisc format, ATRAC is a lossy audio codec which offers near-CD sound quality with relatively small file sizes.

ATRAC3™ A later version of the ATRAC format that squeezes music into even smaller files. It was used for music storage in some portable Sony digial music players.

ATRAC3plus™ The most recent version of the ATRAC codec. ATRAC3plus was found on Sony’s Hi-MD portable recorders and offered even better sound quality at lower bitrates than earlier versions.

AU ( An audio format commonly used for posting sound clips on the Internet. AU files can be played back on Windows, Macintosh, and other operating systems.

AVCHD A high-definition digital video format that can record in 1080i and 720p and still maintain a reasonably small file size. AVCHD files are based on the MPEG4 codec.

AVI (example.avi) A file format for storing and playing back movie clips with sound on Windows-based PCs. AVI is the type of file that’s created when DV clips are imported from a digital camcorder to a PC.


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Bitrate With audio compression, the average amount of data required to store one second of music (expressed in kilobits per second, or Kbps). Some codecs like MP3, WMA, and AAC allow files to be encoded at different bitrates. Generally, as bitrate decreases, so does the sound quality of the resulting file, as well as the amount of memory required to store it.

BMP (example.bmp) A standard format used for storing images on Windows-based PCs. BMP images can either be compressed or uncompressed. This type of file also sometimes appears with the “.DIB” extension.

BZ2 Is a compression program similar in nature to GZIP and ZIP.


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Codec A codec is a way of compressing and decompressing digital files. Each codec uses a slightly different set of algorithms to accomplish this.

Container format A container format is one that holds different kinds of data within its file. Container formats, such as RealAudio and TIFF, are gaining in popularity because of their multimedia applications, as well as their cross-platform compatibility.

CWK (example.cwk) A ClarisWorks (or AppleWorks) document. Can be word processing, spreadsheet, database, presentation program, drawing program, etc.


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DIR (example.dir) Some systems use the DIR extension for directories or folders.

DMF Used for storing vector fonts.

DOC (example.doc) Generic extension indicating some sort of document, usually from Microsoft Word. Variants include DOCX and DOCM.

DV (example.dv) DV is the format used by many digital camcorders, usually on Mini DV cassettes.

DivX DivX was developed by DivX, Inc., to compress a great deal of video content into relatively small files and still retain reasonably good image quality when played back. DivX is based on MPEG-4, and is a popular choice for sending video files over the Internet.


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ETD An Adobe e-book download file is not an e-book itself, but rather a series of instructions that a computer will be able to use to download an e-book and load into an e-book reader.

EXE (example.exe) An executable is a program for a Windows machine.


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FLA (example.fla) A Macromedia Flash source document.

FLAC (Free Lossless Audio Codec) FLAC is a lossless audio codec developed by Josh Coalson and the Xiph.Org Foundation. FLAC can provide full, CD-quality audio in about half the space of the original file. FLAC is considered a lossless container format.

FM ( FrameMaker native document.


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GIF (example.gif) A format for storing digital images, commonly used for bullets, icons, and other graphics on the Web. A single GIF file can combine several frames together for basic animated motion.

GZ and Z (example.gz and example.z) The GNU Zip program is used to compress the size of a single file, or multiple files.


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HEX Generic extension indicating some sort of hexadecimal data.

HTML (example.html) Hypertext Markup Language file contains hypertext capable of being read and interpreted by a browser.


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ICS (example.ics) A file extension with calendar information useable on any machine that support iCalendar standard.

IFF (example.iff) The image file format that works across multiple platforms.

INDD (example.indd) Abode InDesign native format document.


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JAVA A file with this extension should be a file written in Java programming language.

JPEG (example.jpeg) JPEG is a lossy codec for storing and transferring full-color digital images that’s often used to post photography and artwork on the Web. A form of this codec known as Motion JPEG is used by some digital cameras and camcorders for storing video clips of relatively small file size.

JS A file with this extension is probably written in the JavaScript programming language.


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KEY An Apple Keynote document. It is a compound document built from XML files.


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LIB (example.lib) Generic extension indicating “library” data.

LIT (example.lit) Microsoft Reader e-book.

Lossless data compression As the name implies, lossless compression retains all of the data of the original file as it’s converted to a smaller file size. Lossless compression is generally preferred for creating high-quality or professional-grade audio and video files where it’s important to retain fine detail.

Lossy data compression With this kind of compression, some of the source file’s information is discarded to conserve space. When the file is decompressed, this information is reconstructed through algorithms, usually resulting in some loss of sound quality or image detail when compared to the original.


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M4B (example.m4b) MPEG4 container specialized for audio books.

MIDI (example.midi) A MIDI file doesn’t contain actual audio data, but rather contains commands that let MIDI-capable synthesizers re-create a specific musical passage. The MIDI protocol has been used for years as a way for electronic musical instruments (like digital keyboards and sequencers) to communicate with each other. They usually appear with the “.MID” filename extension.

MPEG (example.mpeg) MPEG stands for Moving Picture Experts Group — a committee that sets international standards for the digital encoding of movies and sound. There are several audio/video formats which bear this group’s name. In addition to their popularity on the Internet, several MPEG formats are used with different kinds of A/V gear:

  • MPEG1. This format is often used in digital cameras and camcorders to capture small, easily transferable video clips. It’s also the compression format used to create Video CDs, and commonly used for posting clips on the Internet. The well-known MP3audio format (see definition below) is part of the MPEG1 codec.
  • MPEG2. Commercially produced DVD movies, home-recorded DVD discs, and most digital satellite TV broadcasts employ MPEG2 video compression to deliver their high-quality picture. MPEG2 is also the form of lossy compression used by TiVo-based hard disk video recorders. It can rival the DV format when it comes to picture quality. MPEG2 is considered a container format.
  • MPEG4. A flexible MPEG container format used for both streaming and downloadable Web content. It’s the video format employed by a growing number of camcorders and cameras.

MP3 (example.mp3) The most popular codec for storing and transferring music. Though it employs a lossy compression system which removes frequencies judged to be essentially inaudible, MP3 still manages to deliver near-CD sound quality in a file that’s only about a tenth or twelfth the size of a corresponding uncompressed WAV file.

mp3Pro An updated version of the original MP3 codec. Small, low-bitrate mp3Pro files contain much more high-frequency detail than standard MP3 files encoded at similar low bitrates.

M3U & M34 A file with this extension could store either audio or movie files. Similar to MPEG.

MOV ( A QuickTime movie that stores both movies and sounds.


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NUMBERS An Apple Numbers document. It is a compound document built from XML files.


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OBJ A relocatable object file is the result of compiling a source file in any several programming languages.

ODB (example.odb) An OpenDocument database file in the OASIS OpenDocument standard.

ODC (example.odc) An OpenDocument chart file in the OASIS OpenDocument standard.

ODF (example.odf) An OpenDocument formula file is a format used for storing mathematical data in the OASIS OpenDocument standard.

ODG & OTG (example.odg & example.otg) An OpenDocument graphics file is the drawing format portion in the OASIS OpenDocument standard.

ODI (example.odi) An OpenDocument image file is the format used for storing image data and is part of the OASIS OpenDocument standard.

ODP & OTP (example.odp & example.otp) An OpenDocument presentation file is the presentation format portion of the OASIS OpenDocument standard.

ODS & OTS (example.ods & example.ots) An OpenDocument spreadsheet file in the OASIS OpenDocument standard.

ODT & OTT (example.odt & An OpenDocument text file is the word-processing format portion of the OASIS OpenDocument standard.

OPF (example.opf) An open e-book package.


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PAGES An Apple Pages document.

PBM A portable bitmap format.

PDB & PRC A Palm package of some type, either a Palm Database or Palm Resource.

PDF (example.pdf) Portable Document Format is a format for storing all manner of documents. PDF documents can contain sounds, animations, and simple images.

PCM (Pulse-code modulation) A method of creating digital versions of analog sounds. During the encoding process, a digital “snapshot” of the analog sound wave is taken at regular intervals.

PNG (example.png) A portable network graphics image format design to replace the GIF format.

PPT (example.ppt) A Microsoft PowerPoint document.

PSD (example.psd) A PhotoShop data image format.


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QuickTime QuickTime is a file format for storing and playing back movies with sound. Though developed and supported primarily by Apple, Inc., this flexible format isn’t limited to Macintosh operating systems — it’s also commonly used in Windows systems and other types of computing platforms. In Windows, QuickTime files usually appear with the “.MOV” filename extension.

QXD (example.qxd) A Quark XPress document.


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RAR (example.rar) File format used for archive purposes.

RAW An image file of minimally processed data received from a digital camera. Most camera manufacturers have their own proprietary version of the RAW image format, and their own file suffixes. Canon, for example, uses “.crw” or “.cr2″ for their version of RAW. Nikon’s RAW files end in “.nef,” while Sony uses “.arw” and “.srf” suffixes.

RM (RealMedia) One of the most popular formats for streaming content on the Internet, RealMedia includes the RealAudio codec for sound clips and RealVideo codec for movies.

RTF A rich-text format file attempts to provide more formatting capabilities than simple ASCII.


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Sampling rate In order to convert an analog signal to a digital file, a series of digital “snapshots,” or samples of the signal are made (see: PCM) Collectively, these samples represent the digital version of the analog sound. The higher the sampling rate, the more accurate the sound reproduction.

SDII (example.sdii) An audio format for Macintosh operating systems which is often employed by pro-quality sound editing software applications. SDII files, like AIFF and WAV files, are capable of storing uncompressed CD-quality audio.

Secure Digital Music Initiative (SDMI) The Secure Digital Music Initiative was established to standardize digital music file specifications throughout the industry. The primary purpose was to create a uniform copyright protection protocol that would work with a variety of digital players, software programs, and download sites. SDMI-compliant devices and files have special coding to recognize and comply with the requirements imposed on copyright-protected materials.

SEA A self-extracting archive that contains compressed data that should decompress itself when run.

SEB A Franklin e-book file.

SFX A self-extracting archive that contains compressed data that should decompress itself when run.

SHN (Shorten) Shorten is a lossless form of compression for digital audio. An SHN file is only about half the size of its original AIFF source. Unlike lossy audio codecs (such as MP3, WMA, etc.), SHN is capable of reproducing the original audio signal in its entirety, without removing frequencies.

SWF (example.swf) A playable Macromedia Flash animation.


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TAR (example.tar) Groups of file are often tarred together so that they may be handled as a single file.

TIFF (example.tiff) TIFF is a flexible container format for digital still images, commonly used in desktop publishing. TIFF images can incorporate various forms of compression (like JPEG), or can be uncompressed.

TXT & TEXT (example.txt & example.text) Generic extension indicating a simple text file (usually ASCII).


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UNI (example.uni) Generic extension usually indicating a simple Unicode text file.


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VBM (example.vbm) A video bitmap file.

Variable Bitrate (VBR) Most newer audio and video codecs employ a technology known as variable-bitrate encoding, which allows resulting files to look and sound better while still retaining a compressed, convenient file size. Essentially, VBR encoding assigns more bits to complexly-detailed portions in the original source, and fewer bits to the simpler portions.

Vorbis (Ogg Vorbis) Vorbis is an “open-source” digital audio compression format — that is, it exists in the public domain and is completely free for commercial or non-commercial use. Because Vorbis is most often used in conjunction with a digital A/V container format known as “Ogg,” it’s usually referred to as “Ogg Vorbis.”


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WAV (example.wav) A standard audio format for Windows operating systems, often used for storing high-quality, uncompressed sound.

WMA (Windows Media Audio) Developed by Microsoft, Windows Media Audio is one of today’s most pervasive Internet audio formats. The Windows Media Audio format features built-in copy protection abilities, unlike MP3. Windows Vista, Microsoft’s current flagship operating system software, contains native support for WMA encoding, enabling users to create their own WMA music files.

WMV (Windows Media Video) Microsoft’s proprietary lossy compression format for motion video. Windows Media Video is used for both streaming and downloading content via the Internet. Microsoft’s Windows Media Player, an application bundled with Windows Vista operating systems, lets you play back and manage a range of audio and video file types, including WMA and WMV.

WP & WPD (example.wp & example.wpd) A WordPerfect document.

WPS (example.wps) A Microsoft Works word processing document.


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XLS (example.xls) An Microsoft Excel spreadsheet document.

XML (example.xml) An extensible markup language file that contains simple ASCII.

Xvid Xvid is an open-source lossy video codec based on MPEG-4. Xvid compresses a great deal of video content into relatively small files, and retains a reasonably good video resolution. It can be used with several different operating systems, and is a popular choice for transferring video over the Internet.


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Z (example.z) A UNIX compression program used to reduce the size of a single file.

ZIP ( A file that has been compressed with either the ZIP or PKZIP program will have a ZIP extension.