Posted 09/24/09 at 02:30:42 PM by Michael Brown

When can a file encapsulate more than one type of data? When it’s a metafile, wrapper, or container file. You might think of a container file as a package or envelope in which other files are housed. Zip files, which can contain documents, photos, videos, software programs, and many other types of files, are one type of container that you encounter frequently.

We’ll limit our discussion here to media container formats. A pure container file specifies how the data is stored, but it doesn’t necessarily know how it was compressed or encoded or even what is required to play back those files. This can lead to confusion when dealing with container files wrapped around media because there’s a chance that the media player you’re using is capable of opening the container but not equipped with the algorithm required to decode the files inside. Although a container can theoretically hold any type of data, most are optimized during development to wrap around particular data groups, e.g., digital audio for music; static images for digital photographs; or digital video interleaved with digital audio, plus subtitles, closed-caption information, and chapter data for movies. Container formats that support video also include the information required to synchronize the various data streams in the file during playback.

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