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

Media Data Atom TypesVideo MediaExtensiontype'avcC''pasp''colr''clap'DescriptionAn H.264 AVCConfigurationBox. This extension is required for H.264 video as definedin ISO/IEC 14496-15. For details, see “AVC Decoder Configuration Atom (‘avcC’)” (page161).Pixel aspect ratio. This extension is mandatory for video formats that use non-squarepixels. For details, see “Pixel Aspect Ratio ('pasp')” (page 159).Color parameters—an image description extension required for all uncompressedY´CbCr video types. For details, see “Color Parameter Atoms ('colr')” (page 161).Clean aperture—spatial relationship of Y´CbCr components relative to a canonicalimage center. This allows accurate alignment for compositing of video images capturedusing different systems. This is a mandatory extension for all uncompressed Y´CbCrdata formats. For details, see “Clean Aperture ('clap')” (page 167).Pixel Aspect Ratio ('pasp')This extension specifies the height-to-width ratio of pixels found in the video sample. This is a required extensionfor MPEG-4 and uncompressed Y´CbCr video formats when non-square pixels are used. It is optional whensquare pixels are used.SizeAn unsigned 32-bit integer holding the size of the pixel aspect ratio atom.TypeAn unsigned 32-bit field containing the four-character code 'pasp'.hSpacingAn unsigned 32-bit integer specifying the horizontal spacing of pixels, such as luma sampling instantsfor Y´CbCr or YUV video.vSpacingAn unsigned 32-bit integer specifying the vertical spacing of pixels, such as video picture lines.The units of measure for the hSpacing and vSpacing parameters are not specified, as only the ratio matters.The units of measure for height and width must be the same, however.Table 4-3 (page 159) shows some common pixel aspect ratios.Table 4-3Common pixel aspect ratiosDescription4:3 square pixels (composite NTSC or PAL)hSpacing1vSpacing12012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.159