A container format (informally, sometimes called a wrapper) or metafile is a

file format A file format is a Computer standard, 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 format, pr ...

that allows multiple data streams to be embedded into a single file, usually along with

metadata Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive ...

for identifying and further detailing those streams. Notable examples of container formats include

archive file In computing, an archive file stores the content of one or more files, possibly compressed, with associated metadata such as file name, directory structure, error detection and correction information, commentary, compressed data archives, sto ...

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

Matroska Matroska (styled Matroška) 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 ...

, MP4, and AVI). Among the earliest

cross-platform Within 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 platform, computing platforms. Some ...

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 AS ...

and the 1985 Interchange File Format.

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 that can open a container must also use an appropriate

codec A codec is a computer hardware or software component 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 o ...

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 Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

'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 sound ...

and

video Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...

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 pict ...

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 refers to multimedia delivered through a Computer network, network for playback using a Media player (disambiguation), media player. Media is transferred in a ''stream'' of Network packet, packets from a Server (computing), ...

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 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 signal ...

. Examples include the JPEG File Interchange Format (JFIF), for containing

JPEG JPEG ( , short for Joint Photographic Experts Group and sometimes retroactively referred to as JPEG 1) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degr ...

data, and

Portable Network Graphics Portable Network Graphics (PNG, officially pronounced , colloquially pronounced ) is a raster graphics, raster-graphics file graphics file format, format that supports lossless data compression. PNG was developed as an improved, non-patented ...

(PNG) formats. 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 are texts representing the contents of the audio in a film, television show, opera or other audiovisual media. Subtitles might provide a transcription or translation of spoken dialogue. Although naming conventions can vary, caption ...

, 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 or Tagged Image File Format, commonly known by the abbreviations TIFF or TIF, is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is w ...

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 driftvariations in the respective clock rates of the transmitting and receiving devices. One cause of bit slip is overflow of a receive buffer that occu ...

, while offsets result in framing errors in cases of bit slip. Some containers are exclusive to audio: * AIFF (

IFF In logic and related fields such as mathematics and philosophy, "if and only if" (often shortened as "iff") is paraphrased by the biconditional, a logical connective between statements. The biconditional is true in two cases, where either both ...

file format, widely used on the

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

platform) * WAV (

RIFF A riff is a short, repeated motif or figure in the melody or accompaniment of a musical composition. Riffs are most often found in rock music, punk, heavy metal music, Latin, funk, and jazz, although classical music is also sometimes based ...

file format, widely used on

Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

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 used for storage, transmission and processing of data: formatted as multi-dimensional arrays (for example a 2D image), or tables. FITS is the most commonl ...

(Flexible Image Transport System) still images, raw data, and associated metadata. *

(Tag Image File Format) still images and associated metadata. *

Macintosh Mac is a brand of personal computers designed and marketed by Apple Inc., Apple since 1984. The name is short for Macintosh (its official name until 1999), a reference to the McIntosh (apple), McIntosh apple. The current product lineup inclu ...

PICT resource (

PICT PICT is a graphics file format introduced on the original Apple Macintosh computer as its standard metafile format. It allows the interchange of graphics (both bitmapped and vector), and some limited text support, between Mac applications, an ...

), superseded by

PDF Portable document format (PDF), standardized as ISO 32000, is a file format developed by Adobe Inc., Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, computer hardware, ...

Mac OS X macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

* Windows Metafile (WMF) = (EMF) Enhanced Metafile * Encapsulated PostScript (EPS) * Computer Graphics Metafile (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 (CDR) *

Scalable Vector Graphics Scalable Vector Graphics (SVG) is an XML-based vector graphics 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 sin ...

(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. ...

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) * ASF (container for Microsoft WMA and WMV, which today usually do not use a container) * AVI (the standard

container, also based on

) * DVR-MS ("Microsoft Digital Video Recording", proprietary video container format developed by Microsoft based on ASF) * Flash Video (FLV, F4V) (container for video and audio from

Adobe Systems Adobe Inc. ( ), formerly Adobe Systems Incorporated, is an American software, computer software company based in San Jose, California. It offers a wide range of programs from web design tools, photo manipulation and vector creation, through to ...

) *

(first platform-independent container format) *

(MKV) (not limited to any coding format, as it can hold virtually anything; it is an

open standard An open standard is a standard that is openly accessible and usable by anyone. It is also a common prerequisite that open standards use an open license that provides for extensibility. Typically, anybody can participate in their development due to ...

container format) * MJ2 - Motion

JPEG 2000 JPEG 2000 (JP2) is an image compression standard and coding system. It was developed from 1997 to 2000 by a Joint Photographic Experts Group committee chaired by Touradj Ebrahimi (later the JPEG president), with the intention of superseding their ...

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 (standard

QuickTime QuickTime (or QuickTime Player) is an extensible multimedia architecture created by Apple, which supports playing, streaming, encoding, and transcoding a variety of digital media formats. The term ''QuickTime'' also refers to the QuickTime Pla ...

video container from

Apple Inc. Apple Inc. is an American multinational corporation and technology company headquartered in Cupertino, California, in Silicon Valley. It is best known for its consumer electronics, software, and services. Founded in 1976 as Apple Comput ...

) *

MPEG program stream Program stream (PS or MPEG-PS) is a container format (digital), container format for multiplexing digital audio, video and more. The PS format is specified in MPEG-1 Part 1 (ISO/IEC 11172-1) and MPEG-2 Part 1, Systems (ISO/IEC standard 13818-1/ITU ...

(standard container for MPEG-1 and MPEG-2

elementary stream An elementary stream (ES) as defined by the MPEG communication protocol is usually the output of an audio encoder or video encoder. An ES contains only one kind of data (e.g. audio, video, or closed caption). An elementary stream is often referred ...

s on reasonably reliable media such as disks; used also on

DVD-Video DVD-Video is a consumer video format used to store digital video on DVDs. DVD-Video was the dominant consumer home video format in most of the world in the 2000s. As of 2024, it competes with the high-definition Blu-ray Disc, while both rece ...

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 (Blu-ray Disc or BD) is a Digital media, digital optical disc data storage format designed to supersede the DVD format. It was invented and developed in 2005 and released worldwide on June 20, 2006, capable of storing several hours of ...

video; typically contains multiple video and audio streams, and an

electronic program guide Electronic programming guides (EPGs) and interactive programming guides (IPGs) are menu-based systems that provide users of television, radio, and other media applications with continuously updated menus that display scheduling information fo ...

) * MP4 (standard audio and video container for the

MPEG-4 MPEG-4 is a group of international standards for the compression of digital audio and visual data, multimedia systems, and file storage formats. It was originally introduced in late 1998 as a group of audio and video coding formats and related ...

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 (standard container for Xiph.org audio formats Vorbis and Opus and video format

Theora Theora is a free lossy video compression format. It was 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 contai ...

) * RM (RealMedia; standard container for

RealVideo RealVideo, also spelled as Real Video, is a suite of proprietary format, proprietary video compression formats developed by RealNetworks — the specific format changes with the version. It was first released in 1997 and was at version 15. RealV ...

and RealAudio) *

WebM WebM is an audiovisual media file format. It is primarily intended to offer a royalty-free alternative to use in the HTML video and the HTML audio elements. It has a sister project, WebP, for images. The development of the format is sponsored by ...

(subset of

, used for web-based media distribution on online platforms; container for royalty-free audio formats Vorbis/ Opus and video formats

VP8 VP8 is an open format, open and royalty-free Video coding format, video compression format released by On2 Technologies in 2008. Initially released as a Proprietary software, proprietary successor to On2's previous VP7 format, VP8 was released a ...

/ VP9/ AV1) There are many other container formats, such as NUT, MXF, GXF, ratDVD, SVI, VOB and DivX Media Format

References

External links