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

Media Data Atom TypesHot Spot Image TracksThe dimensions of the hot spot panoramic image are usually the same as those of the image track’s panoramicimage, but this is not required. The dimensions must, however, have the same aspect ratio as the image track’spanoramic image. A hot spot image track should be 8 bits deep.Low-Resolution Image TracksIt’s possible to store one or more low-resolution versions of a panoramic image in a movie file; those versionsare called low-resolution image tracks. If there is not enough memory at runtime to use the normal imagetrack, QuickTime VR uses a lower resolution image track if one is available. A low-resolution image track containsdiced frames just like the higher resolution track, but the reconstructed panoramic image is half the heightand half the width of the higher resolution image.Important The panoramic images in the lower resolution image tracks and the hot spot image tracks, ifpresent, must have the same orientation (horizontal or vertical) as the panorama image track.Track Reference Entry StructureSince there are no fields in the pano sample data atom to indicate the presence of low-resolution image tracks,a separate sibling atom must be added to the panorama sample atom container. The track reference arrayatom contains an array of track reference entry structures that specify information about any low-resolutionimage tracks contained in a movie. Its atom type is kQTVRTrackRefArrayAtomType ('tref').A track reference entry structure is defined by the QTVRTrackRefEntry data type:typedef struct QTVRTrackRefEntry {UInt32UInt16UInt32trackRefType;trackResolution;trackRefIndex;} QTVRTrackRefEntry;Field descriptionstrackRefTypeThe track reference type.trackResolutionThe track resolution.trackRefIndexThe index of the track reference.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.301