Boxes/atoms format

File Format
Name	Boxes/atoms format
Ontology	Electronic File Formats Metaformats Boxes/atoms format

Boxes/atoms format is our name for the metaformat used by JPEG 2000, QuickTime, and other formats. (We also call it Box file format, which is apparently the name used by JPEG XT.) It is a tagged, segmented, hierarchical format, similar to IFF and RIFF. In some descriptions of it, the primary data structure is called a box, and in others it's called an atom.

Format details

A file consists of a sequence of one or more boxes. Some boxes contain data, and some contain other boxes. The only way to tell which is which is to have knowledge of the specific application format.

A box begins with a header of either 8 or (rarely) 16 bytes. The first four bytes of the header are a field we'll call size32. The next four are the Box Type code, usually corresponding to four ASCII characters. Sometimes, the Box Type field is followed by an 8-byte size64 field. Following the header is the payload data.

The size fields use big-endian byte order. They include the size of the header. The size of a box's payload data is determined as follows:

size32	size64	Box payload size
0	not present	Payload extends to the end of the file
1	≥16	(size64 − 16) bytes
2–7 (reserved)
≥8	not present	(size32 − 8) bytes

Variations

Boxes/atoms format is independently defined by each specification that uses it. There are some slight differences in the various formulations of it. For example, for QuickTime, a size32 of 0 is only allowed for top-level boxes. For JPEG 2000, it is also allowed for a box whose parent has a size32 of 0.

Brands

Most (but not all) boxes/atoms-based formats use an "ftyp" box, and along with it a concept called "brands". A brand is a four-letter code representing a format or subformat. Each file has a major brand (or primary brand), and also a compatibility list of brands. A brand's presence in the compatibility list indicates that a decoder which supports that brand can usefully decode the file in some way, even if it doesn't fully support it. This can be useful, though it makes it more complicated to explain just exactly what format a given file is in.

• List of registered brands

Brand cross-reference

This table lists some of the known brands. There are many more brands that are not listed here.

Brand	Description	Refer to
3g[a-z]?		3GP
3g2?		3G2
avc1		AVC (file format)
avif		AVIF
f4v		F4V
heic		HEIF
isom iso2 iso[3-9]		ISO Base Media File Format
jp2		JP2
jpm		JPM
jpx		JPX
jpxb	Baseline JPX	JPX
jpxt		JPEG XT
M4A		AAC
mif1		HEIF
mj2s	MJ2 Simple Profile	MJ2
mjp2		MJ2
mp41		MP4
mp42		MP4
piff		Protected Interoperable File Format
qt		QuickTime
crx		Canon RAW 3
jph		HTJ2K

UUID boxes

Some formats support private extensions using box type "uuid". In a uuid box, the first 16 bytes of what would normally be the payload data are a UUID (arbitrary 16-byte identifier). The real payload data begins immediately after the UUID.

Some of the known UUIDs are listed below. They are not necessarily official in any sense, and they should not be assumed to be meaningful in every format.

UUID	Format	Reference
0537cdab-9d0c-4431-a72a-fa561f2a113e	Exif	ExifTool
2c4c0100-8504-40b9-a03e-562148d6dfeb	Photoshop Image Resources	ExifTool
33c7a4d2-b81d-4723-a0ba-f1a3e097ad38	IPTC-IIM
8974dbce-7be7-4c51-84f9-7148f9882554	PIFF Track Encryption Box	PIFF specification
96a9f1f1-dc98-402d-a7ae-d68e34451809	GeoJP2 World File Box	GeoJP2 specification
a2394f52-5a9b-4f14-a244-6c427c648df4	PIFF Sample Encryption Box	PIFF specification
b14bf8bd-083d-4b43-a5ae-8cd7d5a6ce03	GeoJP2 GeoTIFF Box	GeoJP2 specification
be7acfcb-97a9-42e8-9c71-999491e3afac	XMP	XMP specification
d08a4f18-10f3-4a82-b6c8-32d8aba183d3	PIFF Protection System Specific Header Box	PIFF specification

Related formats

• ISO Base Media File Format
• JPEG 2000
• MP4
• QuickTime

See also Category:Box file format.