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

Movie AtomsReference MoviesCPU Speed AtomA CPU speed atom specifies the minimum computing power needed to display a movie. QuickTime performsan internal test to determine the speed of the user’s computer.This is not a simple measurement of clock speed—it is a measurement of performance for QuickTime-relatedoperations. Speed is expressed as a relative value between 100 and 2^31, in multiples of 100.Note Typical scores might range from a minimum score of 100, which would describe a computeras slow as, or slower than, a 166 MHz Pentium or 120 MHz PowerPC, to a maximum score of 600 fora 500 MHz Pentium III or 400 MHz G4 PowerPC. A computer with a graphics accelerator and aGigahertz clock speed might score as high as 1000. Future computers will score higher.Applications should play the movie with the highest specified CPU speed that is less than or equal to the user’sspeed. If the user’s speed is lower than any movie’s CPU speed, applications should play the movie with thelowest CPU speed requirement. The movie with the highest CPU speed is assumed to be the highest quality.Only one CPU speed atom is allowed in a given reference movie descriptor atom.A CPU speed atom may contain the following fields:SizeThe number of bytes in this CPU speed atom.TypeThe type of this atom; this field must be set to 'rmcs'.FlagsA 32-bit integer that is currently always 0.CPU speedA relative ranking of required computer speed, expressed as a 32-bit integer divisible by 100, with largernumbers indicating higher speed.Version Check AtomA version check atom specifies a software package, such as QuickTime or QuickTime VR, and the version ofthat package needed to display a movie. The package is specified using a Macintosh Gestalt type, such a'qtim' for QuickTime (QuickTime provides support for these Gestalt tests in the Windows computingenvironment).You can specify a minimum required version to be returned by the Gestalt check, or you can require that aspecific value be returned after performing a binary AND operation on the Gestalt bitfield and a mask.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.124