Glossary
ISO BMFF box
A box, sometimes called an atom, is the nested container unit that HEIC, MP4 and MOV files are built from.
Updated
Also written: atom, ISO Base Media File Format.
These formats are trees. Each box has a size and a four-character type, and boxes nest inside one another to describe the file. Metadata occupies its own boxes within that tree, and in the QuickTime convention location is written to a box whose name begins with the copyright character — which is why generic EXIF tools miss it.
Offsets are what make editing delicate. HEIC records the exact byte position of every item in an iloc table, so deleting metadata bytes would invalidate every offset after that point. The safe approach is to overwrite the metadata payload in place with zeros: the file stays structurally valid, every offset still resolves, and the image data is never touched.
That is why a cleaned HEIC comes back the same size as the original. The metadata is gone; its former space is zeroed rather than reclaimed.
A container can also carry more than one copy of the same information, in both a metadata box and a separate user-data section — so clearing one and not the other leaves the question open.
Related terms
- Chunk — A chunk is a self-describing section of a file, carrying its own type label and length.
- RIFF chunk — A RIFF chunk is a labelled, length-prefixed block in the container format WebP is built on.
- Container format — A container format is the file structure that wraps compressed image or video data together with the metadata describing it.