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

Movie AtomsTrack AtomsAlthough the result of applying the clean aperture and the pixel aspect ratio is what is intended for final display,there are cases where it is useful to display all the pixels that exist in the content for various differentpurposes. Readers parsing QuickTime movies require information allowing these different display modes inorder to provide this flexibility:Clean ModeIn this mode both the clean aperture and the pixel aspect ratio are applied. The dimensions of the trackbecome equal to the clean dimensions which are equal to the display dimensions (with conformedcontents).Production ModeThis mode applies the pixel aspect ratio but not the clean aperture. The image is presented in the correctaspect ratio, but the extra pixels outside of the image that exists in the source material will be presented.The track dimensions are equal to the result of applying the pixel aspect ratio.Classic ModeThis mode displays the image without applying either the pixel aspect ratio or the clean aperture. Theimage is displayed using the track header dimensions, meaning the decompressed picture is scaled intothe track header dimensions if the encoded dimensions are different.Encoded PixelsThe encoded pixels are displayed intact in this mode. Under this mode the track dimensions are equalto the encoded dimensions. No scaling or transformation takes place.The information needed for each of these presentation modes are represented in the optional track aperturemode dimensions atoms.Note Older applications built prior to QuickTime 7 will continue to use the dimension values storedin the track header.Track Aperture Mode Dimensions AtomA container atom that stores information for video correction in the form of three required atoms. This atomis optionally included in the track atom. The type of the track aperture mode dimensions atom is ‘tapt’.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.62