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

Media Data Atom TypesSound MediaThe uLaw (mu-law) encoding scheme is used on North American and Japanese phone systems, and iscoming into use for voice data interchange, and in PBXs, voice-mail systems, and Internet talk radio (viaMIME). In uLaw encoding, 14 bits of linear sample data are reduced to 8 bits of logarithmic data.The aLaw encoding scheme is used in Europe and the rest of the world.The kULawCompression and the kALawCompression formats are typically found in .au formats.Floating-Point FormatsBoth kFloat32Format and kFloat64Format are floating-point uncompressed formats. Depending uponcodec-specific data associated with the sample description, the floating-point values may be in big-endian(network) or little-endian (Intel) byte order. This differs from the 16-bit formats, where there is a single formatfor each endian layout.24- and 32-Bit Integer FormatsBoth k24BitFormat and k32BitFormat are integer uncompressed formats. Depending upon codec-specificdata associated with the sample description, the floating-point values may be in big-endian (network) orlittle-endian (Intel) byte order.kMicrosoftADPCMFormat and kDVIIntelIMAFormat Sound CodecsThe kMicrosoftADPCMFormat and the kDVIIntelIMAFormat codec provide QuickTime interoperabilitywith AVI and WAV files. The four-character codes used by Microsoft for their formats are numeric. To constructa QuickTime-supported codec format of this type, the Microsoft numeric ID is taken to generate a four-charactercode of the form 'msxx' where xx takes on the numeric ID.kDVAudioFormat Sound CodecThe DV audio sound codec, kDVAudioFormat, decodes audio found in a DV stream. Since a DV frame containsboth video and audio, this codec knows how to skip video portions of the frame and only retrieve the audioportions. Likewise, the video codec skips the audio portions and renders only the image.kQDesignCompression Sound CodecThe kQDesignCompression sound codec is the QDesign 1 (pre-QuickTime 4) format. Note that there is alsoa QDesign 2 format whose four-character code is 'QDM2'.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.188