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A container format (informally, sometimes called a wrapper) or metafile is a
file format A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are used to encode information in a digital storage medium. File formats may be either proprietary or free. Some file format ...
that allows multiple data streams to be embedded into a single file, usually along with
metadata Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive metadata – the descriptive ...
for identifying and further detailing those streams. Notable examples of container formats include archive files (such as the ZIP format) and formats used for multimedia playback (such as Matroska, MP4, and
AVI Avi is a given name, usually masculine, often a diminutive of Avram, Avraham, etc. It is sometimes feminine and a diminutive of the Hebrew spelling of Abigail. People with the given name include: * Avi (born 1937), Newbery award-winning Americ ...
). Among the earliest
cross-platform In computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software ...
container formats were Distinguished Encoding Rules and the 1985
Interchange File Format Interchange File Format (IFF), is a generic container file format originally introduced by Electronic Arts in 1985 (in cooperation with Commodore) in order to facilitate transfer of data between software produced by different companies. IFF f ...
.


Design

Although containers may identify how data or metadata is encoded, they do not actually provide instructions about how to decode that data. A
program Program, programme, programmer, or programming may refer to: Business and management * Program management, the process of managing several related projects * Time management * Program, a part of planning Arts and entertainment Audio * Programm ...
that can open a container must also use an appropriate
codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...
to decode its contents. If the program doesn't have the required algorithm, it can't use the contained data. In these cases, programs usually emit an error message that complains of a missing codec, which users may be able to acquire. Container formats can be made to wrap any kind of data. Though there are some examples of such file formats (e.g.
Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...
's DLL files), most container formats are specialized for specific data requirements. For example, since
audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of sou ...
and
video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) sy ...
streams can be coded and decoded with many different algorithms, a container format may be used to provide the appearance of a single file format to users of multimedia playback software.


Considerations

The differences between various container formats arise from five main issues: # Popularity; how widely supported a container is. # Overhead. This is the difference in file-size between two files with the same content in a different container. # Support for advanced codec functionality. Older formats such as AVI do not support new codec features like B-frames, VBR audio or VFR video natively. The format may be "hacked" to add support, but this creates compatibility problems. # Support for advanced content, such as chapters, subtitles, meta-tags, user-data. # Support of
streaming media Streaming media is multimedia that is delivered and consumed in a continuous manner from a source, with little or no intermediate storage in network elements. ''Streaming'' refers to the delivery method of content, rather than the content i ...
.


Single coding formats

In addition to pure container formats, which specify ''only'' the wrapper but not the coding, a number of file formats specify ''both'' a storage layer and the coding, as part of
modular design Modular design, or modularity in design, is a design principle that subdivides a system into smaller parts called ''modules'' (such as modular process skids), which can be independently created, modified, replaced, or exchanged with other modules ...
and forward compatibility. Examples include JPEG File Interchange Format (JFIF) for containing
JPEG JPEG ( ) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and imag ...
data, and
Portable Network Graphics Portable Network Graphics (PNG, officially pronounced , colloquially pronounced ) is a raster-graphics file format that supports lossless data compression. PNG was developed as an improved, non-patented replacement for Graphics Interchange ...
(PNG). In principle, coding can be changed while the storage layer is retained; for example, Multiple-image Network Graphics (MNG) uses the PNG container format but provides animation, while JPEG Network Graphics (JNG) puts JPEG encoded data in a PNG container; in both cases however, the different formats have different magic numbers – the format specifies the coding, though a MNG can contain both PNG-encoded images and JPEG-encoded images.


Multimedia container formats

The container file is used to identify and interleave different data types. Simpler container formats can contain different types of audio formats, while more advanced container formats can support multiple audio and video streams,
subtitles Subtitles and captions are lines of dialogue or other text displayed at the bottom of the screen in films, television programs, video games or other visual media. They can be transcriptions of the screenplay, translations of it, or informa ...
, chapter-information, and meta-data ( tags) — along with the synchronization information needed to play back the various streams together. In most cases, the file header, most of the metadata and the synchro chunks are specified by the container format. For example, container formats exist for optimized, low-quality, internet video streaming which differs from high-quality Blu-ray streaming requirements. Container format parts have various names: "chunks" as in RIFF and PNG, "atoms" in QuickTime/MP4, "packets" in MPEG-TS (from the communications term), and "segments" in JPEG. The main content of a chunk is called the "data" or "payload". Most container formats have chunks in sequence, each with a header, while
TIFF Tag Image File Format, abbreviated TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is widely supported by scanning, faxing, word process ...
instead stores offsets. Modular chunks make it easy to recover other chunks in case of file corruption or dropped frames or
bit slip In digital transmission, bit slip is the loss or gain of a bit or bits, caused by clock drift – variations in the respective clock rates of the transmitting and receiving devices. One cause of bit slippage is overflow of a receive buffer that ...
, while offsets result in framing errors in cases of bit slip. Some containers are exclusive to audio: *
AIFF Audio Interchange File Format (AIFF) is an audio file format standard used for storing sound data for personal computers and other electronic audio devices. The format was developed by Apple Inc. in 1988 based on Electronic Arts' Interchange ...
( IFF file format, widely used on Mac OS platform) * WAV (
RIFF A riff is a repeated chord progression or refrain in music (also known as an ostinato figure in classical music); it is a pattern, or melody, often played by the rhythm section instruments or solo instrument, that forms the basis or acc ...
file format, widely used on
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for se ...
platform) * XMF (Extensible Music Format) Other containers are exclusive to still images: *
FITS Flexible Image Transport System (FITS) is an open standard defining a digital file format useful for storage, transmission and processing of data: formatted as multi-dimensional arrays (for example a 2D image), or tables. FITS is the most commo ...
(Flexible Image Transport System) still images, raw data, and associated metadata. *
TIFF Tag Image File Format, abbreviated TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is widely supported by scanning, faxing, word process ...
(Tagged Image File Format) still images and associated metadata. *
Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
PICT resource ( PICT), superseded by
PDF Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. ...
in
Mac OS X macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lap ...
*
Windows Metafile Windows Metafile (WMF) is an image file format originally designed for Microsoft Windows in the 1990s. The original Windows Metafile format was not device-independent (though could be made more so with placement headers) and may contain both vect ...
(WMF) = (EMF) Enhanced Metafile *
Encapsulated PostScript Encapsulated PostScript (EPS) is a Document Structuring Convention (DSC) conforming PostScript document format usable as a graphics file format. The format was developed as early as 1987 by John Warnock and Chuck Geschke, the founders of Ado ...
(EPS) *
Computer Graphics Metafile Computer Graphics Metafile (CGM) is a free and open international standard file format for 2D vector graphics, raster graphics, and text, and is defined by ISO/IEC 8632. Overview All graphical elements can be specified in a textual source ...
(CGM) *
Portable Document Format Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating syste ...
(PDF) *
Corel Draw File CorelDRAW is a vector graphics editor developed and marketed by Corel, Corel Corporation. It is also the name of the Corel graphics suite, which includes the bitmap-image editor Corel Photo-Paint as well as other graphics-related programs (see be ...
(CDR) * Scalable Vector Graphics (SVG) *
Rich Text Format ) As an example, the following RTF code would be rendered as follows: This is some bold text. Character encoding A standard RTF file can only consist of 7-bit ASCII characters, but can use escape sequences to encode other characters. T ...
file (RTF) Other flexible containers can hold many types of audio and video, as well as other media. The most popular multi-media containers are: *
3GP 3GP (3GPP file format) is a multimedia container format defined by the Third Generation Partnership Project (3GPP) for 3G UMTS multimedia services. It is used on 3G mobile phones but can also be played on some 2G and 4G phones. 3G2 (3GPP2 ...
(used by many mobile phones; based on the ISO base media file format) * ASF (container for Microsoft WMA and
WMV Windows Media Video (WMV) is a series of video codecs and their corresponding video coding formats developed by Microsoft. It is part of the Windows Media framework. WMV consists of three distinct codecs: The original video compression technology ...
, which today usually do not use a container) *
AVI Avi is a given name, usually masculine, often a diminutive of Avram, Avraham, etc. It is sometimes feminine and a diminutive of the Hebrew spelling of Abigail. People with the given name include: * Avi (born 1937), Newbery award-winning Americ ...
(the standard
Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...
container, also based on
RIFF A riff is a repeated chord progression or refrain in music (also known as an ostinato figure in classical music); it is a pattern, or melody, often played by the rhythm section instruments or solo instrument, that forms the basis or acc ...
) *
DVR-MS DVR-MS (''Microsoft Digital Video Recording'') is a proprietary video and audio file container format, developed by Microsoft used for storing TV content recorded by Windows XP Media Center Edition, Windows Vista and Windows 7. Multiple dat ...
("Microsoft Digital Video Recording",
proprietary {{Short pages monitor