.MOV File Format – Metadata

meta

Unlike the ISO meta box, Apple’s meta atom is a plain container with no version and flags. If the handler type is not mdta, another specification defines the contents: the iTunes-style tags in M4A and many MP4 files use handler mdir, with item atoms named ©nam, ©ART and so on instead of key indexes. Unknown atoms inside ilst are ignored; uuid atoms may appear wherever a list of atoms is allowed.

hdlr and mhdr

mhdr: version and flags (0), then nextItemID (uint32), the next unique item ID to assign, normally one more than the largest used. 0xFFFFFFFF means new IDs must be found by searching for an unused value. (Apple’s field list spells the type mdhr in one place; the atom is mhdr.)

keys

Keys are numbered from 1; 0 is never an index. Namespace mdta uses reverse-DNS key names; namespace udta uses a user data four-character code. Apple’s example table holds three keys:

ilst, items and data

ilst holds one item atom per value. An item’s type is not a four-character code but the 1-based key index as a uint32, so key 1’s item has type 0x00000001. An item holds:

For example, an item for key 1 whose value is the UTF-8 text “Hello”:

00 00 00 1D 00 00 00 01                 item: size 29, key index 1
00 00 00 15 64 61 74 61                 data: size 21
00 00 00 01 00 00 00 00                 type 1 (UTF-8), default locale
48 65 6C 6C 6F                          “Hello”

A writer that does not want to limit a value to certain countries uses the ISO 3166 reserved code ZZ; for any language, und. A locale matches when both country and language match, a 0 matching anything.

ctry and lang

Both are full atoms (version and flags, then a uint32 count of lists). Each list is a uint16 count and that many uint16 codes: ISO 3166 two-letter codes in ctry, packed ISO 639-2/T codes in lang. Lists are referred to by 1-based index from data atoms; at most 255 codes per atom. Apple’s example lang holds two lists: 5575, 6721, 4277 (eng, fra, deu) and 19969, 16882 (spa, por).

Well-known types

QuickTime metadata keys

All in namespace mdta. Text values are UTF-8 (type 1) and may have several values for different languages and countries.

A direction is a compass heading in degrees, optionally signed and optionally followed by M for magnetic, then optionally a slash and an elevation angle; in the example, 20.34° magnetic, 5.3° below the horizontal.