.MOV File Format – Movie atoms

moov

A container. It must hold a movie header (mvhd), a compressed movie (cmov) or a reference movie (rmra); an uncompressed movie atom may hold both mvhd and rmra.

mvhd

The atom is 108 bytes. Apple documents only version 0. Files that also follow ISO/IEC 14496-12 may use version 1, where creation time, modification time and duration are 64-bit (the same change as in the MP4 mvhd), making the atom 120 bytes.

ctab

Up to 256 preferred colours for showing the movie on a 256-colour display, as a Macintosh colour table.

clip and crgn

clip, in a movie or a track, holds one clipping region atom, crgn, whose data is a QuickDraw region:

Compressed movie: cmov, dcom, cmvd

Since QuickTime 3 the movie resource may be compressed losslessly. The moov atom then holds only cmov, which holds two atoms:

Uncompressed, the data is a complete moov atom. Apple’s documentation does not list the dcom codes; files in practice use zlib (zlib-wrapped Deflate), which is how FFmpeg reads them. Treat any other code as unknown.

Reference movies: rmra and rmda

A reference movie lists alternative movies, each with the requirements for playing it. The player picks the best one the system can play, falling back down the list if a reference cannot be resolved, and finally to the movie in mvhd if there is one. rmra holds one or more reference movie descriptor atoms, rmda, each holding:

For a movie import component, the component flags that may be required are canMovieImportInPlace, movieImportSubTypeIsFileExtension (the subtype is a file extension such as DOC ) and canMovieImportFiles. Treat every resolved reference as untrusted input.

udta: user data

A udta atom in a movie, track or media holds a list of atoms, one per item. Only one udta may be the direct child of a given moov or trak. Unknown items are skipped. The display items (WLOC, LOOP, SelO, AllF, ptv ) count only in the movie’s own user data.

The © character is byte 0xA9. Keyword items exist for text whose sort order cannot be worked out from the display text, as in some East Asian languages.

International text items

Every item whose type starts with © holds one or more strings, each in its own small record so one item can carry several translations:

tnam

A track may have several tnam atoms in different languages.

ptv

The movie plays full screen with no window or controller, the rest of the screen black, until the user presses Esc.

tagc

The payload is one tag: 7-bit ASCII letters, digits, -, ., _ and ~, not null-terminated, compared case-sensitively. Public tags start public.; private tags start with a reversed domain such as com.example.. Other prefixes are reserved. The public tags defined are:

Other user data types registered with the MP4 Registration Authority, including the 3GPP asset items and camera items such as manu, modl and swre, are listed on Data types and codes.