Quicktime File Format (2012-08-14).pdf

Media Data Atom TypesTween MediaTween Sample DataTween sample data is stored in QT atom structures.At the root level, there are one or more tween entry atoms; these atoms have an atom type value of 'twen'.Each tween entry atom completely describes one interpolation operation. These atoms should be consecutivelynumbered starting at 1, using the atom ID field.Each tween entry atom contains several more atoms that describe how to perform the interpolation. The atomID field in each of these atoms must be set to 1.Tween start atom (atom type is 'twst').This atom specifies the time at which the interpolation is to start. The time is expressed in the media’stime coordinate system. If this atom is not present, the starting offset is assumed to be 0.Tween duration atom (atom type is 'twdu').This atom specifies how long the interpolation is to last. The time is expressed in the media’s timecoordinate system. If this atom is not present, the duration is assumed to be the length of the sample.Tween data atom (atom type is 'twdt').This atom contains the actual values for the interpolation. The contents depend on the value of the tweentype atom.Tween type atom (atom type is 'twnt').Describes the type of interpolation to perform.Table 4-15 (page 236) shows all currently defined tween types. All tween types are currently supported usinglinear interpolation.Table 4-15Tween type valuesTween type16-bit integer32-bit integer32-bit fixed-pointPoint: two 16-bit integersRectangle: four 16-bit integersQuickDraw regionValue123456Tween dataTwo 16-bit integers.Two 32-bit integers.Two 32-bit fixed-point numbers.Two points.Two rectangles.Two rectangles and a region. The tween entry atom mustcontain a 'qdrg' atom with an atom ID value of 1. Theregion is transformed through the resulting matrices.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.236