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 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, 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 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 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's DLL files), most container formats are specialized for specific data requirements. For example, since audio 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-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.

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

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 bicondi ...

file format, widely used on Mac OS platform) * WAV ( RIFF 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 ...

platform) * XMF (Extensible Music Format) Other containers are exclusive to still images: * FITS (Flexible Image Transport System) still images, raw data, and associated metadata. * TIFF (Tagged Image File Format) still images and associated metadata. * Macintosh PICT resource ( PICT), superseded by PDF in Mac OS X * 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 CorelDRAW is a vector graphics editor developed and marketed by 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 below) ...

(CDR) * Scalable Vector Graphics (SVG) * Rich Text Format 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, which today usually do not use a container) *

(the standard Microsoft Windows container, also based on RIFF) * 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) *

(first platform-independent container format) * Matroska (MKV) (not limited to any coding format, as it can hold virtually anything; it is an open standard container format) * MJ2 - Motion JPEG 2000 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 video container from Apple Inc.) * MPEG program stream (standard container for MPEG-1 and MPEG-2 elementary streams on reasonably reliable media such as disks; used also on DVD-Video 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 video; typically contains multiple video and audio streams, and an electronic program guide) * MP4 (standard audio and video container for the MPEG-4 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 Xiph.Org Foundation is a nonprofit organization that 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 de ...

audio formats Vorbis and Opus and video format Theora) * RM (RealMedia; standard container for RealVideo and RealAudio) * WebM (subset of Matroska, used for web-based media distribution on online platforms; container for royalty-free audio formats Vorbis/ Opus and video formats VP8/ VP9/ AV1) There are many other container formats, such as NUT, MXF, GXF, ratDVD, SVI,

VOB VOB (for video object) is the container format in DVD-Video media. VOB can contain digital video, digital audio, subtitles, DVD menus and navigation contents multiplexed together into a stream form. Files in VOB format may be encrypted. File fo ...

and DivX Media Format

References

External links