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

Profile Atom GuidelinesUniversal FeaturesBrandCodeDescriptionProfile Parent0x20202020avbr“Audio Variable Bit Rate Indication” (page 418)Movie or Sound Track0x20202020achc“Audio Channel Count” (page 419)Movie or Sound TrackMaximum Video Bit RateContaining profile atomTrack (video), movieReserved0x00000000part-ID0x20202020 (universal feature)feature-code'mvbr'feature-valueUnsigned int(32) indicating maximum video bit rate in bits per secondFeature ValuesThe value is an unsigned 32-bit integer indicating the maximum video bit rate in bits per second. The valuemay be larger than the actual video bit rate, so it should not be interpreted as a bit rate that will actually occur.Example: 1 Mbps = 1000000.Writer ResponsibilitiesA writer of the maximum video bit rate should record a value that is equal to or greater than the actual bit ratefor the video track. A writer (such as a CE device) may choose to record a constant value so long as that valueis greater than or equal to the bit rate that may be encoded. It is also permitted to record a value set by thevideo encoder during initialization, so long as the value is never exceeded.Feature Value AlgorithmApple recommends a sliding average over 1 second calculated from the sample tables.If the feature is written for a newly encoded track (as by a CE device), it is permitted to record a value used toinitialize the video encoder so long as the value is never exceeded. If the video track is edited and the maximumvideo bit rate recalculated, it may be calculated as a sliding average over 1 second, based on the sample table.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.399