A container or wrapper format is a meta

Meta

Meta- , is a prefix used in English to indicate a concept which is an abstraction from another concept, used to complete or add to the latter....

-file format

File format

A file format is a particular way that information is encoded for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa. There are different kinds of formats for...

 whose specification describes how different data elements and metadata

Metadata

The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...

 coexist in a computer file

Computer file

A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...

.

Among the earliest cross-platform

Cross-platform

In computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...

 container formats were Distinguished Encoding Rules

Distinguished Encoding Rules

Distinguished Encoding Rules , is a message transfer syntax specified by the ITU in X.690. The Distinguished Encoding Rules of ASN.1 is an International Standard drawn from the constraints placed on basic encoding rules encodings by X.509. DER encodings are valid BER encodings...

 and the 1985 Interchange File Format

Interchange File Format

Interchange File Format , is a generic container file format originally introduced by the Electronic Arts company in 1985 in order to ease transfer of data between software produced by different companies....

. Containers are frequently used in multimedia

Multimedia

Multimedia is media and content that uses a combination of different content forms. The term can be used as a noun or as an adjective describing a medium as having multiple content forms. The term is used in contrast to media which use only rudimentary computer display such as text-only, or...

 applications.

Properties

Since the container does not describe how data or metadata is encoded, a program

Computer program

A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

 able to identify and open a container file might not be able to decode the contained data. This may be caused by the program lacking the required decoding algorithm

Codec

A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...

, or the meta-data not providing enough information.

By definition, a container format could wrap any kind of data. Though there are some examples of such file formats (e.g. Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

's DLL

Dynamic-link library

Dynamic-link library , or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems...

 files), most container formats are specialized for specific data requirements. For example, a popular family of containers is found for use with multimedia file formats. Since audio

Audio file format

An audio file format is a file format for storing digital audio data on a computer system. This data can be stored uncompressed, or compressed to reduce the file size. It can be a raw bitstream, but it is usually a container format or an audio data format with defined storage layer.-Types of...

 and video streams can be coded and decoded with many different algorithms, a container format may be used to provide only a single file to the user.

Multimedia container formats

The container file is used to identify and interleave

Interleaving

In computer science and telecommunication, interleaving is a way to arrange data in a non-contiguous way to increase performance.It is typically used:* In error-correction coding, particularly within data transmission, disk storage, and computer memory....

 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

Subtitle (captioning)

Subtitles are textual versions of the dialog in films and television programs, usually displayed at the bottom of the screen. They can either be a form of written translation of a dialog in a foreign language, or a written rendering of the dialog in the same language, with or without added...

, chapter-information, and meta-data (tags

Tag (metadata)

In online computer systems terminology, a tag is a non-hierarchical keyword or term assigned to a piece of information . This kind of metadata helps describe an item and allows it to be found again by browsing or searching...

) — 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 DVD 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 instead stores offsets. Modular chunks make it easy to recover other chunks in case of file corruption or dropped frames or bit slip

Bit slip

In digital transmission, bit slip is the loss of a bit or bits, caused by clock drift – variations in the respective clock rates of the transmitting and receiving devices....

, while offsets result in framing errors

Serial communications

In telecommunication and computer science, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels...

 in cases of bit slip.

Some containers are exclusive to audio:

• AIFF (IFF file format, widely used on Mac OS
  Mac OS
  Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...
  
   platform)
• WAV
  WAV
  Waveform Audio File Format , is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs...
  
    (RIFF file format, widely used on Windows
  Microsoft Windows
  Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
  
   platform)
• XMF
  Extensible Music Format (XMF)
  XMF is a tree-based digital container format used to bundle music-oriented content, such as a MIDI file and optionally the sounds it uses, liner notes or other content grouped by language-codes....
  
   (Extensible Music Format)

Other containers are exclusive to still images:

• FITS
  FITS
  Flexible Image Transport System is a digital file format used to store, transmit, and manipulate scientific and other images. FITS is the most commonly used digital file format in astronomy...
  
   (Flexible Image Transport System) still images, raw data, and associated metadata.
• TIFF
  Tagged Image File Format
  TIFF is a file format for storing images, popular among graphic artists, the publishing industry, and both amateur and professional photographers in general. As of 2009, it is under the control of Adobe Systems...
  
   (Tagged Image File Format) still images and associated metadata.

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
  3GP is a multimedia container format defined by the Third Generation Partnership Project for 3G UMTS multimedia services. It is used on 3G mobile phones but can also be played on some 2G and 4G phones....
  
   (used by many mobile phones; based on the ISO base media file format
  ISO base media file format
  ISO base media file format defines a general structure for time-based multimedia files such as video and audio. It is used as the basis for other media file formats...
  
  )
• ASF
  Advanced Systems Format
  Advanced Systems Format is Microsoft's proprietary digital audio/digital video container format, especially meant for streaming media...
  
   (container for Microsoft WMA
  Windows Media Audio
  Windows Media Audio is an audio data compression technology developed by Microsoft. The name can be used to refer to its audio file format or its audio codecs. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs...
  
   and WMV
  Windows Media Video
  'Windows Media Video is a video compression format for several proprietary codecs developed by Microsoft. The original video format, known as WMV, was originally designed for Internet streaming applications, as a competitor to RealVideo. The other formats, such as WMV Screen and WMV Image, cater...
  
  , which today usually do not use a container)
• AVI
  Audio Video Interleave
  Audio Video Interleave , known by its acronym AVI, is a multimedia container format introduced by Microsoft in November 1992 as part of its Video for Windows technology. AVI files can contain both audio and video data in a file container that allows synchronous audio-with-video playback...
  
   (the standard Microsoft Windows
  Microsoft Windows
  Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
  
   container, also based on RIFF)
• DVR-MS
  DVR-MS
  DVR-MS 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....
  
   ("Microsoft Digital Video Recording", proprietary
  Proprietary software
  Proprietary software is computer software licensed under exclusive legal right of the copyright holder. The licensee is given the right to use the software under certain conditions, while restricted from other uses, such as modification, further distribution, or reverse engineering.Complementary...
  
   video container format developed by Microsoft based on ASF
  Advanced Systems Format
  Advanced Systems Format is Microsoft's proprietary digital audio/digital video container format, especially meant for streaming media...
  
  )
• Flash Video (FLV, F4V) (container for video and audio from Adobe Systems
  Adobe Systems
  Adobe Systems Incorporated is an American computer software company founded in 1982 and headquartered in San Jose, California, United States...
  
  )
• IFF
  Interchange File Format
  Interchange File Format , is a generic container file format originally introduced by the Electronic Arts company in 1985 in order to ease transfer of data between software produced by different companies....
  
   (first platform-independent container format)
• Matroska
  Matroska
  The Matroska Multimedia Container is an open standard free container format, a file format that can hold an unlimited number of video, audio, picture or subtitle tracks in one file. It is intended to serve as a universal format for storing common multimedia content, like movies or TV shows...
  
   (MKV) (not limited to any codec or system, as it can hold virtually anything. It is an open standard
  Open standard
  An open standard is a standard that is publicly available and has various rights to use associated with it, and may also have various properties of how it was designed . There is no single definition and interpretations vary with usage....
  
   and open source
  Open source
  The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
  
   container format).
• MJ2 - Motion JPEG 2000
  JPEG 2000
  JPEG 2000 is an image compression standard and coding system. It was created by the Joint Photographic Experts Group committee in 2000 with the intention of superseding their original discrete cosine transform-based JPEG standard with a newly designed, wavelet-based method...
  
   file format, based on the ISO base media file format which is defined in MPEG-4 Part 12 and JPEG 2000 Part 12
• QuickTime File Format
  QuickTime File Format
  QuickTime File Format is a computer file format used natively by the QuickTime framework.- Design :The format specifies a multimedia container file that contains one or more tracks, each of which stores a particular type of data: audio, video, effects, or text...
  
   (standard QuickTime
  QuickTime
  QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...
  
   video container from Apple Inc.)
• MPEG program stream (standard container for MPEG-1 and MPEG-2 elementary stream
  Elementary stream
  An elementary stream as defined by MPEG communication protocol is usually the output of an audio or video encoder. ES contains only one kind of data, e.g. audio, video or closed caption. An elementary stream is often referred to as "elementary", "data", "audio", or "video" bitstreams or streams...
  
  s on reasonably reliable media such as disks; used also on DVD-Video
  DVD-Video
  DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in Asia, North America, Europe, and Australia. Discs using the DVD-Video specification require a DVD drive and a MPEG-2 decoder...
  
   discs)
• MPEG-2 transport stream (a.k.a. MPEG-TS) (standard container for digital broadcasting and for transportation over unreliable media; used also on Blu-ray Disc
  Blu-ray Disc
  Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
  
   video; typically contains multiple video and audio streams, and an electronic program guide
  Electronic program guide
  Electronic program guides and interactive program guides provide users of television, radio, and other media applications with continuously updated menus displaying broadcast programming or scheduling information for current and upcoming programming...
  
  )
• MP4
  MPEG-4 Part 14
  MPEG-4 Part 14 or MP4 is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images...
  
   (standard audio and video container for the MPEG-4
  MPEG-4
  MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...
  
   multimedia portfolio, based on the ISO base media file format defined in MPEG-4 Part 12 and JPEG 2000 Part 12) which in turn was based on the QuickTime file format.
• Ogg
  Ogg
  Ogg is a free, open container format maintained by the Xiph.Org Foundation. The creators of the Ogg format state that it is unrestricted by software patents and is designed to provide for efficient streaming and manipulation of high quality digital multimedia.The Ogg container format can multiplex...
  
   (standard container for Xiph.org
  Xiph.Org Foundation
  Xiph.Org Foundation is a non-profit organizationthat produces free multimedia formats and software tools. It focuses on the Ogg family of formats, the most successful of which has been Vorbis, an open and freely licensed audio format and codec designed to compete with the patented MP3 and AAC...
  
   audio fomat Vorbis
  Vorbis
  Vorbis is a free software / open source project headed by the Xiph.Org Foundation . The project produces an audio format specification and software implementation for lossy audio compression...
  
   and video format Theora
  Theora
  Theora is a free lossy video compression format. It is developed by the Xiph.Org Foundation and distributed without licensing fees alongside their other free and open media projects, including the Vorbis audio format and the Ogg container....
  
  )
• RM
  RealMedia
  RealMedia is a proprietary multimedia container format created by RealNetworks. Its extension is ".rm". It is typically used in conjunction with RealVideo and RealAudio and is used for streaming content over the Internet....
  
   (RealMedia; standard container for RealVideo
  RealVideo
  RealVideo is a suite of proprietary video compression formats developed by RealNetworks – the specific format changes with the version. It was first released in 1997 and is at version 10. RealVideo is supported on many platforms, including Windows, Mac, Linux, Solaris, and several mobile...
  
   and RealAudio
  RealAudio
  RealAudio is a proprietary audio format developed by RealNetworks and first released in April 1995. It uses a variety of audio codecs, ranging from low-bitrate formats that can be used over dialup modems, to high-fidelity formats for music. It can also be used as a streaming audio format, that is...
  
  )

There are many other container formats, such as NUT, MXF, GXF, ratDVD

RatDVD

ratDVD is a proprietary media container file type that supports the same features as DVD-Video. Unlike other container formats like Matroska, it is designed to accurately mirror the exact feature set of standard DVDs, facilitating round-tripping back to the DVD-Video format...

, SVI, VOB

VOB

A VOB file is a container format in DVD-Video media. VOB can contain video, audio, subtitle, menu and navigation contents multiplexed together into a stream form. VOB is based on the MPEG program stream format, but with additional limitations and specifications in the private streams...

 and DivX Media Format

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

Modular design, or "modularity in design" is an approach that subdivides a system into smaller parts that can be independently created and then used in different systems to drive multiple functionalities...

 and forward compatibility

Forward compatibility

Forward compatibility or upward compatibility is a compatibility concept for systems design, as e.g. backward compatibility. Forward compatibility aims at the ability of a design to gracefully accept input intended for later versions of itself...

.

Examples include JPEG File Interchange Format

JPEG File Interchange Format

The JPEG File Interchange Format is an image file format standard. It is a format for exchanging JPEG encoded files compliant with the JPEG Interchange Format standard. It solves some of JIFs limitations in regard to simple JPEG encoded file interchange...

 (JFIF) for containing JPEG

JPEG

In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....

 data, and Portable Network Graphics (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

Magic number (programming)

In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:* A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures...

 – the format specifies the coding, though a MNG can contain both PNG-encoded images and JPEG-encoded images.

Issues

The differences between various container formats arise from five main issues:

1. Popularity; how widely supported a container is.
2. Overhead. This is the difference in file-size between two files with the same content in a different container.
3. Support for advanced codec functionality. Older formats such as AVI do not support new codec features like B-frames, VBR
   Variable bitrate
   Variable bitrate is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate , VBR files vary the amount of output data per time segment...
   
    audio or VFR
   Variable frame rate
   Variable frame rate is a term in video compression for a feature supported by some container formats which allows for the frame rate to change actively during video playback, or to drop the idea of frame rate completely and set individual timecode for each frame...
   
    video natively. The format may be "hacked" to add support, but this creates compatibility problems.
4. Support for advanced content, such as chapters, subtitles, meta-tags, user-data.
5. Support of streaming media
   Streaming media
   Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
   
   

See also

• Comparison of (audio/video) container formats
  Comparison of container formats
  This table compares features of container formats. To see which multimedia players support which container format, look at comparison of media players.-Information:-Audio formats supported:-Video formats supported:-Caption formats supported:...
  
  
• Open source codecs and containers
  Open source codecs and containers
  This is a listing of open-source implementations of media formats—usually called codecs. Many of the codecs listed implement media formats that are restricted by patents and are henceforth not open formats. For example, x264 is a widely used open source implementation of the heavily patent...
  
  
  • FFmpeg
    FFmpeg
    FFmpeg is a free software project that produces libraries and programs for handling multimedia data. The most notable parts of FFmpeg are libavcodec, an audio/video codec library used by several other projects, libavformat, an audio/video container mux and demux library, and the ffmpeg command line...
    
    , cross-platform
    Cross-platform
    In computing, cross-platform, or multi-platform, is an attribute conferred to computer software or computing methods and concepts that are implemented and inter-operate on multiple computer platforms...
    
    , open source
    Open source
    The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
    
    , audio and video codec suite/library
    Codec
    A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...
    
    
• List of multimedia (audio/video) codecs
  • Comparison of video codecs
    Comparison of video codecs
    A video codec is software or a device that provides encoding and decoding which may or may not include the use of video compression and/or decompression for digital video....
    
    
  • Comparison of audio codecs
    Comparison of audio codecs
    The following tables compare general and technical information for a variety of audio formats and audio compression formats. For listening tests comparing the perceived audio quality of audio formats and codecs, see the article Codec listening test....
    
    

External Links

• Online Video File Format Identification Tool - Designed primarily for CCTV video formats and codecs