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

Media Data Atom TypesTimecode MediaMPEG-1 Layer 3 (MP3) CodecsThe QuickTime MPEG layer 3 (MP3) codecs come in two particular flavors, as shown in Table 4-7 (page 176).The first (kMPEGLayer3Format) is used exclusively in the constant bit rate (CBR) case (pre-QuickTime 4). Theother (kFullMPEGLay3Format) is used in both the CBR and variable bit rate (VBR) cases. Note that they arethe same codec underneath.MPEG-4 AudioMPEG-4 audio is stored as a sound track with data format 'mp4a' and certain additions to the sound sampledescription and sound track atom. Specifically:●●The compression ID is set to -2 and redefined sample tables are used (see “Redefined Sample Tables” (page180)).The sound sample description includes an siDecompressionParam atom (see “siDecompressionParamAtom ('wave')” (page 185)). The siDecompressionParam atom includes:●An MPEG-4 elementary stream descriptor extension atom (see “MPEG-4 Elementary Stream DescriptorAtom ('esds')” (page 186)).●The inclusion of a format atom is strongly recommended. See “Format Atom ('frma')” (page 185).●The last atom in the siDecompressionParam atom must be a terminator atom. See “TerminatorAtom (0x00000000)” (page 185).●Other atoms may be present as well; unknown atoms should be ignored.The audio data is stored as an elementary MPEG-4 audio stream, as defined in ISO/IEC specification 14496-1.Formats Not Currently in Use: MACE 3:1 and 6:1These compression formats are obsolete: MACE 3:1 and 6:1.These are 8-bit sound codec formats, defined as follows:kMACE3Compression = FOUR_CHAR_CODE('MAC3'), /*MACE 3:1*/kMACE6Compression = FOUR_CHAR_CODE('MAC6'), /*MACE 6:1*/Timecode MediaTimecode media is used to store time code data in QuickTime movies. It has a media type of 'tmcd'.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.189