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Acontainer format (informally, sometimes called awrapper) ormetafile is afile format that allows multiple data streams to be embedded into a singlefile, usually along withmetadata for identifying and further detailing those streams.[1] Notable examples of container formats includearchive files (such as theZIP format) and formats used for multimedia playback (such asMatroska,MP4, andAVI). Among the earliestcross-platform container formats wereDistinguished Encoding Rules and the 1985Interchange File Format.
Although containers may identify how data or metadata is encoded, they do not actually provide instructions about how to decode that data. Aprogram that can open a container must also use an appropriatecodec 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'sDLL files), most container formats are specialized for specific data requirements. For example, sinceaudio andvideo 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.
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The differences between various container formats arise from five main issues:
In addition to pure container formats, which specifyonly the wrapper but not the coding, a number of file formats specifyboth a storage layer and the coding, as part ofmodular design andforward compatibility.
Examples include theJPEG File Interchange Format (JFIF), for containingJPEG data, andPortable Network Graphics (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, whileJPEG Network Graphics (JNG) puts JPEG encoded data in a PNG container; in both cases however, the different formats have differentmagic numbers – the format specifies the coding, though a MNG can contain both PNG-encoded images and JPEG-encoded images.
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, whileTIFF instead stores offsets. Modular chunks make it easy to recover other chunks in case of file corruption or dropped frames orbit slip, while offsets result inframing errors in cases of bit slip.
Some containers are exclusive to audio:
Other containers are exclusive to still images:
Other flexible containers can hold many types of audio and video, as well as other media. The most popular multi-media containers are:[2][3]
There are many other container formats, such asNUT,MXF,GXF,ratDVD, SVI,VOB andDivX Media Format