Atoms, Boxes, Parents, Children & hex (oh my) An MPEG-4 file is made of a number of discrete units called atoms (well, they were called atoms in the first version of the specification, now they are prosaically called 'boxes'). An atom has a format: Anything beyond that basic 8 bytes is either optional & defined by the hierarchy it is found in (moov.udta.meta.XXXX atoms have a format defined by Qui