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 formats ...

that allows multiple data streams to be embedded into a single

file File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...

, 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 file In computing, an archive file is a computer file that is composed of one or more files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compre ...

s (such as the ZIP format) and formats used for multimedia playback (such as

Matroska Matroska is a project to create a container format that can hold an unlimited number of video, audio, picture, or subtitle tracks in one file. The Matroska Multimedia Container is similar in concept to other containers like AVI, MP4, or Adva ...

, MP4, and AVI). 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 r ...

container formats were

Distinguished Encoding Rules X.690 is an ITU-T standard specifying several ASN.1 encoding formats: * Basic Encoding Rules (BER) * Canonical Encoding Rules (CER) * Distinguished Encoding Rules (DER) The Basic Encoding Rules (BER) were the original rules laid out by the ASN.1 s ...

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 fil ...

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 * Progra ...

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 da ...

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 serv ...

'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) syste ...

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-frame In the field of video compression a video frame is compressed using different algorithms with different advantages and disadvantages, centered mainly around amount of data compression. These different algorithms for video frames are called pi ...

s, 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 it ...

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 and

forward compatibility Forward compatibility or upward compatibility is a design characteristic that allows a system to accept input intended for a later version of itself. The concept can be applied to entire systems, electrical interfaces, telecommunication signals, ...

. Examples include

JPEG File Interchange Format The JPEG File Interchange Format (JFIF) is an image file format standard published as ITU-T Recommendation T.871 and ISO/IEC 10918-5. It defines supplementary specifications for the container format that contains the image data encoded with the JP ...

(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 F ...

(PNG). In principle, coding can be changed while the storage layer is retained; for example,

Multiple-image Network Graphics Multiple-image Network Graphics (MNG) is a graphics file format, published in 2001, for animated images. Its specification is publicly documented and there are free software reference implementations available. MNG is closely related to the ...

(MNG) uses the PNG container format but provides animation, while

JPEG Network Graphics JPEG Network Graphics (JNG, ) is a JPEG-based graphics file format which is closely related to Portable Network Graphics, PNG: it uses the PNG file structure (with a different signature) as a Container format (digital), container format to wrap J ...

(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 informati ...

, 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 processin ...

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

(

IFF In logic and related fields such as mathematics and philosophy, "if and only if" (shortened as "iff") is a biconditional logical connective between statements, where either both statements are true or both are false. The connective is bicon ...

file format, widely used on

Mac OS Two major famlies of Mac operating systems were developed by Apple Inc. In 1984, Apple debuted the operating system that is now known as the "Classic" Mac OS with its release of the original Macintosh System Software. The system, rebranded "M ...

platform) *

WAV Waveform Audio File Format (WAVE, or WAV due to its filename extension; pronounced "wave") is an audio file format standard, developed by IBM and Microsoft, for storing an audio bitstream on PCs. It is the main format used on Microsoft Wind ...

(

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 accompani ...

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 serv ...

platform) *

XMF XMF (Extensible Music Format) 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. The first XMF definiti ...

(Extensible Music Format) Other containers are exclusive to still images: * FITS (Flexible Image Transport System) still images, raw data, and associated metadata. *

(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 The Picts were a group of peoples who lived in what is now northern and eastern Scotland (north of the Firth of Forth) during Late Antiquity and the Early Middle Ages. Where they lived and what their culture was like can be inferred from ear ...

), 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. ...

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 (computer), Mac computers. Within the market of ...

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 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 vector ...

* Encapsulated PostScript (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 systems. ...

(PDF) * Corel Draw File (CDR) *

Scalable Vector Graphics Scalable Vector Graphics (SVG) is an XML-based vector image format for defining two-dimensional graphics, having support for interactivity and animation. The SVG specification is an open standard developed by the World Wide Web Consortium sinc ...

(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. Th ...

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 (used by many mobile phones; based on the

ISO base media file format The ISO base media file format (ISOBMFF) is a container file format that defines a general structure for files that contain time-based multimedia data such as video and audio. It is standardized in ISO/IEC 14496-12, a.k.a. MPEG-4 Part 12, and wa ...

) *

ASF ASF may refer to: Arts and entertainment * Alabama Shakespeare Festival, a drama festival * ''Asimov's Science Fiction'', a U.S.-based English-language science fiction magazine containing SF stories Science and technology Biological * A ...

(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 (the standard

container, also based on

) *

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 data st ...

("Microsoft Digital Video Recording",

proprietary {{Short pages monitor