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The File Extension Library

What is a file extension?

Short answer: it's the set of letters after the period (.) in the name of a file.

Long answer: File extensions signify the file format of a file. It tells the operating system (OS) how data was stored in the file. Not all OS, require a file extension though. For instance, this is optional in Unix, but is mandatory with MS-DOS and Windows systems.

In most file formats the file type is actually defined by the contents (first bytes, file structure), but extensions are used to define the application that is used for opening the file.

Below is a detailed database of thousands of file extensions our team has compiled for you. Feel free to browse!


Browse all Extensions:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
U - Extension Details
Date Added: February 01, 2009
File Extension:  .U
Description 1: A file with the extension .U means it is a Subsampled Raw YUV video playback file. The files are the result of producing MPEG video format files. People can view these files using a variety of MPEG and videocompliant viewers like the Apple QuickTime. A split PPM file consists of three files: .U, .V and .Y files. Stanford MPEG codec uses the YUV representation.
Description 2: .U files bear an audio container format that is generally used in storing ?encoded audio data. Sun Microsystems introduced the format, but MusicKit also utilizes it for the NeXT operating system. A .U file features a header containing an optional info section, six 32bit words, as well as audio data. File extension .AU is typically seen attached to AU files.
File Type:   Audio file
Mode: Binary
Program(s) to Open:  Windows: edit with Epic Games UnrealEd Macintosh: Apple QuickTime Player, Microsoft Windows Media Player, RealNetworks Real Player
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