Edit List Atoms

QuickTime Movie File Format Specification, May 1996

Edit List Atoms

You use the edit list atom, shown in Figure 0-13 , to map from a time in a movie to a time in a media, and ultimately to media data. This information is in the form of an edit list table, shown in Figure 0-14 . Edit list atoms have an atom type value of 'elst' .

Edit list atoms contain the following data elements.

Size: A 32-bit integer that specifies the number of bytes in this edit list atom.
Type: A 32-bit integer that identifies the atom type; this field must be set to 'elst' .
Version: A 1-byte specification of the version of this edit list atom.
Flags: Three bytes of space for flags. Set this field to 0.
Number of entries: A 32-bit integer that specifies the number of entries in the edit list atom that follows.
Edit list table: An array of 32-bit values grouped into entries containing 3 values each.

Figure 14 The layout of an edit list table

An edit list table contains the following elements.

Track duration: A 32-bit integer that specifies the duration of this edit segment in units of the movie's time scale.
Media time: A 32-bit integer containing the starting time within the media of this edit segment (in media time scale units). If this field is set to -1, it is an empty edit. The last edit in a track should never be an empty edit. Any difference between the movie's duration and the track's duration is expressed as an implicit empty edit.
Media rate: A 32-bit fixed-point number that specifies the relative rate at which to play the media corresponding to this edit segment. This rate value cannot be 0 or negative.