Container format (digital)

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A container format is a computer file format that can contain various types of data, compressed by means of standardized audio/video codecs. The container file is used to identify and interleave the different data types. Simpler container formats can contain different types of audio codecs, 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.

Some containers are exclusive to audio:

WAV (RIFF file format, widely used on Windows platform)
AIFF (IFF file format, widely used on Mac OS platform)

Other flexible containers can hold many types of audio and video, as well as other media. The most popular multi-media containers are:

IFF (first platform independent container format)
AVI (the standard Microsoft Windows container, also based on RIFF)
ASF (standard container for Microsoft WMA and WMV)
DVR-MS ("Microsoft Digital Video Recording", proprietary video container format developed by Microsoft based on ASF)
- DVR-MS uses MPEG-2 standard video and audio using MPEG-1 Layer II or Dolby Digital AC-3 (ATSC A/52)
MOV (standard QuickTime video container from Apple Inc.)
MPEG-2 transport stream (TS) (a.k.a. MPEG-TS) (standard container for digital broadcasting; typically contains multiple video and audio streams, and an electronic program guide) and program stream (PS)
MP4 (standard audio and video container for the MPEG-4 multimedia portfolio)
Ogg (Vorbis, standard audio container for Xiph.org codecs)
OGM ("Ogg Media", standard video container for Xiph.org codecs)
RealMedia (standard container for RealVideo and RealAudio)
Matroska / MKV (not standard for any codec or system, but it is an open standard and open source container format).
3gp (used by many mobile phones)

There are many other container formats, such as , NUT, MPEG, MXF, ratDVD, SVI, VOB, and DivX Media Format (DMF) .divx

Other containers are exclusive to still images:

the TIFF (Tagged Image File Format) is a wrapper file format for still images and associated metadata.
the Flexible Image Transport System is a wrapper file format for still images, raw data, and associated metadata.

See the Comparison of container formats for details regarding these formats.

[edit] Issues

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, VFR natively, although the format may be "hacked" to add support, creating compatibility problems.
Support for advanced content, such as chapters, subtitles, meta-tags, user-data.
Support of streaming media