File format

A file format is a particular layout of data in a computer file. Some file formats have well-defined and publicly available specifications, but others may be described only within the software that processes them. Some file formats define strong rules as to what can be in them. A JPEG cannot hold anything but image data for example, but an AVI can hold audio or video data, frequently both. Files are typically stored in a file system.

• Audio file formats
  • AIFF
  • au
  • CDDA (audio data as written to an ISO9660 CD)
  • IFF-8SVX
  • IFF-16SV
  • MP2
  • MP3
  • RAW (raw samples without any header or sync)
  • Ogg (Ogg Vorbis, similar in principle to MP3)
  • WAV
  • WMA
  • Music formats
    • MID (standard MIDI file; most often just notes but occasionally also sample dumps)
  • NSF (bytecode program to play NES music)
    • MOD (Soundtracker and Protracker sample and melody modules)
    • S3M (ScreamTracker 3 module, with a few more effects and a dedicated volume column)
    • XM (FastTracker module, adding instrument envelopes)
    • IT (Impulse Tracker module, adding compressed samples, note-release actions, and more effects including a resonant filter)
• Document formats - These are ways of storing mainly text
  • ASCII (.txt)
  • Amigaguide
  • HTML (.html, .htm)
  • Microsoft Word DOC (Format revised and altered very often; little official documentation)
  • RTF (a textual encoding of the data in a Word DOC; many programs' Word export filters actually write RTF as RTF is much easier to generate reliably)
  • TeX
  • Troff
  • XML
• Image or graphics file formats
  • GIF
  • IFF-ILBM (.lbm)
  • JNG (single-frame MNG with JPEG data)
  • JPEG JFIF (.jpg)
  • PCX
  • PNG
  • PSD
  • TIFF (.tif)
• Object code file formats
  • a.out
  • ELF
  • MZ EXE (.exe; used in MS-DOS)
  • PE (.exe; used in Microsoft Windows and some other systems)
• Page description languages
  • dvi
  • pcl
  • PDF
  • PostScript (.ps, .ps.gz)
• Scene description languages
  • RenderMan
  • VRML
• Hypertext description
  • HTML
  • CSS
• Data exchange
  • XML
• Archivation and compression formats
  • arj
  • bzip2 (.bz2)
  • gzip (.gz)
  • lzh
  • lzx
  • pkzip (.zip)
  • rar
  • tar
  • zoo
• Video file formats
  • Animated GIF (simple animation)
  • ASF (ASF is a shell, which enables any form of compression to be used, MPEG4 is common)
  • AVI (AVI is a shell, which enables any form of compression to be used, MPEG and a variation on MPEG4 are common)
  • MNG (mainly simple animation containing PNG and JPEG objects, often somewhat more complex than animated GIF)
  • MPEG
  • Ogg (once the MNG and Tarkin codecs mature)
  • QuickTime
  • RealMedia
• Disk images (a file system used as a random-access archive file inside another file system; extensions include .img and .iso)

Some file formats may be used for more than one type of content. For example GIF can store both pictures and simple animations, and avi can store almost any type of multimedia. The Ogg format can potentially store video and/or audio, but actual implementations are currently rare as of December 2001, and only an audio codec called Ogg Vorbis exists for the format, though developers continue to work on video codecs such as the Tarkin video codec and to integrate other formats such as MNG (lossless and motion JPEG compression), FLAC (lossless audio compression), and XML (text-based data such as captions and subtitles) into the Ogg framework. IFF is a now defunct format which, like AVI, is a shell, but IFF had no limitations, being able to store sound, image, movie, animation, data or archive. If a programmer wanted to store data in the IFF format, he just had to define the subformat following the general rules. For example, WAV files follow a variation of IFF called RIFF.

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A good source of information on file formats is the Wotsit archive at http://www.wotsit.org