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

Media Data Atom TypesVideo MediaThe clean aperture extension contains a width in pixels, a height in picture lines, and a horizontal and verticaloffset between the stored image center and a canonical image center for the given video system. The widthis typically the width of the canonical clean aperture for a video system divided by the pixel aspect ratio of thestored data. The offsets also take into account any “overscan” in the stored image. The height and width mustbe positive values, but the offsets may be positive, negative, or zero.These values are given as ratios of two 32-bit numbers, so that applications can calculate precise values withminimum roundoff error. For whole values, the value should be stored in the numerator field while thedenominator field is set to 1.SizeA 32-bit unsigned integer containing the size of the 'clap' atom.TypeA 32-bit unsigned integer containing the four-character code 'clap'.apertureWidth_N (numerator)A 32-bit signed integer containing either the width of the clean aperture in pixels or the numeratorportion of a fractional width.apertureWidth_D (denominator)A 32-bit signed integer containing either the denominator portion of a fractional width or the number1.apertureHeight_N (numerator)A 32-bit signed integer containing either the height of the clean aperture in picture lines or the numeratorportion of a fractional height.apertureHeight_D (denominator)A 32-bit signed integer containing either the denominator portion of a fractional height or the number1.horizOff_N (numerator)A 32-bit signed integer containing either the horizontal offset of the clean aperture center minus(width–1)/2 or the numerator portion of a fractional offset. This value is typically zero.horizOff_D (denominator)A 32-bit signed integer containing either the denominator portion of the horizontal offset or the number1.vertOff_N (numerator)A 32-bit signed integer containing either the vertical offset of the clean aperture center minus (height–1)/2or the numerator portion of a fractional offset. This value is typically zero.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.168