ISO Base Media File Format
ISO Base Media File Format (occasionally abbreviated BMFF) is a metaformat for "time-based" media formats (mainly audio and video). It is based on the more-general metaformat we're calling boxes/atoms format.
It is defined by Part 12 of the MPEG-4 standard, and also by Part 12 of the JPEG 2000 standard.
Files always have an "ftyp" box, which contains a list of "brands" that give information about the specific file format. See the boxes/atoms article for more about brands.
Much of the format was copied from QuickTime format.
Among the formats based on it are MJ2 and MP4.
Identification
Files use boxes/atoms format, and almost always have both an "ftyp" box and an "moov" box. However, for compatibility with certain older files, the "ftyp" box can sometimes be omitted if the brand would be "mp41".
