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What is it?

ISO Media files (ISO/IEC 14496-12) are a container layout, formatted in a simple-yet-complex way.

The ISO container format is derived from Apple's QuickTime File Format.

Boxing it up

At the most-basic, each unit of an ISO file is called a Box. A Box is a length-prefixed chunk of bytes. Putting the length first makes it incredibly easy to skip over unneeded portions of the file.

Every box has a type. These are usually chosen as human-readable strings of four characters; you may have heard the term FourCC used in older formats (e.g. RIFF files).

There are a small set of top-level boxes.

See [Box Cutter] for more details.