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

Media Data Atom TypesVideo MediaAVC Decoder Configuration Atom (‘avcC’)This atom contains an MPEG-4 decoder configuration atom. This is a required extension to the video sampledescription for H.264 video. This extension appears in video sample descriptions only when the codec type is‘avc1’.Note The decoder configuration record that this atom contains is defined in the MPEG-4 specificationISO/IEC FDIS 14496-15.SizeAn unsigned 32-bit integer holding the size of the AVC decoder configuration atom.TypeAn unsigned 32-bit field containing the four-character-code 'avcC'.AVC Decoder Configuration RecordAn AVCDecoderConfigurationRecord for H.264 video, as defined in the MPEG-4 specification ISO/IEC14496-15, and subject to the restrictions for storage in an MPEG-4 file, also specified in ISO/IEC 14496-15.Color Parameter Atoms ('colr')This atom is a required extension for uncompressed Y´CbCr data formats. The 'colr' extension is used tomap the numerical values of pixels in the file to a common representation of color in which images can becorrectly compared, combined, and displayed. The common representation is the CIE XYZ tristimulus values(defined in Publication CIE No. 15.2).Use of a common representation also allows you to correctly map between Y´CbCr and RGB color spaces andto correctly compensate for gamma on different systems.The 'colr' extension supersedes the previously defined 'gama' Image Description extension. Writers ofQuickTime files should never write both into an Image Description, and readers of QuickTime files shouldignore 'gama' if 'colr' is present.The 'colr' extension is designed to work for multiple imaging applications such as video and print. Eachapplication, driven by its own set of historical and economic realities, has its own set of parameters needed tomap from pixel values to CIE XYZ.The CIE XYZ representation is mapped to various stored Y´CbCr formats using a common set of transfer functionsand matrixes. The transfer function coefficients and matrix values are stored as indexes into a table of canonicalreferences. This provides support for multiple video systems while limiting the scope of possible values to aset of recognized standards.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.161