diff --git a/ALACMagicCookieDescription.txt b/ALACMagicCookieDescription.txt deleted file mode 100644 index c15550b..0000000 --- a/ALACMagicCookieDescription.txt +++ /dev/null @@ -1,241 +0,0 @@ -__________________________________________________________________________________________________________________________________ -__________________________________________________________________________________________________________________________________ -Apple Lossless Format "Magic Cookie" Description -__________________________________________________________________________________________________________________________________ -__________________________________________________________________________________________________________________________________ - -Many encoded formats for audio require additional, codec specific configuration information in order to operate successfully. -This codec specific information is often called a 'magic cookie'. The Apple Lossless codec's 'magic cookie' contains the -ALACSpecificConfig and optional ALACChannelLayoutInfo (both described below). - -The 'magic cookie' must accompany the bitstream when stored in any file container (M4A/MP4, CAF) so that it may be provided to the -decoder when decoding the bitstream. From the caller's perspective, the 'magic cookie' is opaque and should be stored in the file -and presented to the decoder exactly as it is vended from the encoder (and consequently stored in the file). - -The ALAC 'magic cookie' as stored in a file has all fields described in big-endian order (regardless of file format). - -The layout of the 'magic cookie' is as follows: - - ----------------- ALAC Specific Info (24 bytes) (mandatory) --------------------------- -(ALACSpecificConfig) Decoder Info - ----------------- Channel Layout Info (24 bytes) (optional) ---------------------------- -(ALAC Channel Layout Info) Channel Layout Info - - -If the channel layout is absent from the cookie, then the following assumptions are made: -1 channel - mono -2 channels - stereo in left, right order -> 2 channels - no specific channel designation or role. - - -__________________________________________________________________________________________________________________________________ -* ALAC Specific Info (24 bytes) (mandatory) -__________________________________________________________________________________________________________________________________ - -The Apple Lossless codec stores specific information about the encoded stream in the ALACSpecificConfig. This -info is vended by the encoder and is used to setup the decoder for a given encoded bitstream. - -When read from and written to a file, the fields of this struct must be in big-endian order. -When vended by the encoder (and received by the decoder) the struct values will be in big-endian order. - -/* - struct ALACSpecificConfig (defined in ALACAudioTypes.h) - abstract This struct is used to describe codec provided information about the encoded Apple Lossless bitstream. - It must accompany the encoded stream in the containing audio file and be provided to the decoder. - - field frameLength uint32_t indicating the frames per packet when no explicit frames per packet setting is - present in the packet header. The encoder frames per packet can be explicitly set - but for maximum compatibility, the default encoder setting of 4096 should be used. - - field compatibleVersion uint8_t indicating compatible version, - value must be set to 0 - - field bitDepth uint8_t describes the bit depth of the source PCM data (maximum value = 32) - - field pb uint8_t currently unused tuning parameter. - value should be set to 40 - - field mb uint8_t currently unused tuning parameter. - value should be set to 10 - - field kb uint8_t currently unused tuning parameter. - value should be set to 14 - - field numChannels uint8_t describes the channel count (1 = mono, 2 = stereo, etc...) - when channel layout info is not provided in the 'magic cookie', a channel count > 2 - describes a set of discreet channels with no specific ordering - - field maxRun uint16_t currently unused. - value should be set to 255 - - field maxFrameBytes uint32_t the maximum size of an Apple Lossless packet within the encoded stream. - value of 0 indicates unknown - - field avgBitRate uint32_t the average bit rate in bits per second of the Apple Lossless stream. - value of 0 indicates unknown - - field sampleRate uint32_t sample rate of the encoded stream - */ - -typedef struct ALACSpecificConfig -{ - uint32_t frameLength; - uint8_t compatibleVersion; - uint8_t bitDepth; - uint8_t pb; - uint8_t mb; - uint8_t kb; - uint8_t numChannels; - uint16_t maxRun; - uint32_t maxFrameBytes; - uint32_t avgBitRate; - uint32_t sampleRate; - -} ALACSpecificConfig; - - -__________________________________________________________________________________________________________________________________ -Channel Layout Info (24 bytes) (optional) -__________________________________________________________________________________________________________________________________ - -The Apple Lossless codec can support a specific set of channel layouts. When channel information is vended -by the encoder (in the 'magic cookie'), it is formatted in the the ALACChannelLayoutInfo. - -When read from and written to a file, the fields of this struct must be in big-endian order. -When vended by the encoder (and received by the decoder) the struct values will be in big-endian order. - -/* - struct ALACChannelLayoutInfo (defined in ALACAudioTypes.h) - abstract This struct is used to specify particular channel orderings or configurations. - It is an optional portion of the 'magic cookie', being required to describe specific channel layouts (see below) - of more than 2 channels. - - field channelLayoutInfoSize uint32_t indicates the size of the channel layout data - value should be set to 24 - - field channelLayoutInfoID uint32_t identifier indicating that channel layout info is present - value = 'chan' - - field versionFlags uint32_t version flags - value should be set to 0 - - field channelLayoutTag uint32_t channel layout type - from defined list in ALACAudioTypes.h (see below) - - field reserved1 uint32_t currently unused field - value should be set to 0 - - field reserved2 uint32_t currently unused field - value should be set to 0 -*/ - -typedef struct ALACChannelLayoutInfo -{ - uint32_t channelLayoutInfoSize; - uint32_t channelLayoutInfoID; - uint32_t versionFlags; - uint32_t channelLayoutTag; - uint32_t reserved1; - uint32_t reserved2; -} ALACChannelLayoutInfo; - - -* Channel Layout Tags - -These constants will be used to describe the bitstream's channel layout. (defined in ALACAudioTypes.h) - -enum -{ - kALACChannelLayoutTag_Mono = (100<<16) | 1, // C - kALACChannelLayoutTag_Stereo = (101<<16) | 2, // L R - kALACChannelLayoutTag_MPEG_3_0_B = (113<<16) | 3, // C L R - kALACChannelLayoutTag_MPEG_4_0_B = (116<<16) | 4, // C L R Cs - kALACChannelLayoutTag_MPEG_5_0_D = (120<<16) | 5, // C L R Ls Rs - kALACChannelLayoutTag_MPEG_5_1_D = (124<<16) | 6, // C L R Ls Rs LFE - kALACChannelLayoutTag_AAC_6_1 = (142<<16) | 7, // C L R Ls Rs Cs LFE - kALACChannelLayoutTag_MPEG_7_1_B = (127<<16) | 8 // C Lc Rc L R Ls Rs LFE (doc: IS-13818-7 MPEG2-AAC) -}; - - -__________________________________________________________________________________________________________________________________ -__________________________________________________________________________________________________________________________________ -* Storing Apple Lossless Magic Cookie in Audio Files -__________________________________________________________________________________________________________________________________ -__________________________________________________________________________________________________________________________________ - -The Apple Lossless Magic Cookie is treated as opaque by file parsing code. The 'magic cookie' vended by the encoder -is placed without modification into the audio file and the read from that file and passed (unmodified) to the decoder. - -__________________________________________________________________________________________________________________________________ -* CAF File - -In a CAF file (Core Audio File), the 'magic cookie' is stored in CAF's Magic Cookie chunk ('kuki'). - -__________________________________________________________________________________________________________________________________ -* MP4/M4A File - -In an MP4/M4A file, the 'magic cookie' is encapsulated in the AudioSample entry of a Sound Description box ('stsd'). -An ISO style full box header to describe the ALACSpecificConfig portion is appended to the AudioSampleEntry, followed by the -'magic cookie' as it is vended by the encoder. - -(All fields are stored in big-endian order: see ISO/IEC 14496-12 for a full description of the SoundDescription and AudioSampleEntry boxes, etc.) - ----------------- SoundDescriptionBox (FullBox) ---------------------------- - - SampleEntrySize // = sizeof(SoundDescriptionBox)(16) + sizeof (AudioSampleEntry)(AudioSampleEntry.SampleEntrySize) - SampleEntryType // = 'stsd' - VersionFlags // = 0 - EntryCount // = 1 - ----------------- Audio Sample Entry (REQUIRED) ----------------------------- - - SampleEntrySize // sizeof(AudioSampleEntry)(36) + sizeof(full ISO box header)(12) + sizeof(Apple Lossless Magic Cookie) - SampleEntryType // = 'alac', specifies that the AudioSampleEntry describes an Apple Lossless bitstream - mReserved[6] // = 0 - dref index // = 1 - reserved[2] // = 0 - channel count // = number of channels as a uint_16 value - sample size // = source pcm bitdepth (example = 16bit source pcm) - predefined // = 0 - reserved // = 0 - sample rate // sample rate as a uint_32 value - - Appended to AudioSampleEntry: - - ALAC Specific Info Size // uint_32 value, = 36 (12 + sizeof(ALACSpecificConfig)) - ALAC Specific Info ID // uint_32 value, = 'alac', format ID which matches the Audio Sample Entry SampleEntryType field - Version Flags // uint_32 value, = 0 - - Apple Lossless Magic Cookie // 'magic cookie' vended from ALAC encoder (24 or 48 Bytes) - -__________________________________________________________________________________________________________________________________ -__________________________________________________________________________________________________________________________________ -* Compatibility -__________________________________________________________________________________________________________________________________ -__________________________________________________________________________________________________________________________________ - -Previous versions of the Apple Lossless encoder vended a different 'magic cookie'. To ensure compatibility, the Apple Lossless decoder -must be prepared to parse a 'magic cookie' in the format described below. Note that the 'magic cookie' defined above is -encapsulated in the following method and can be extracted as a contiguous set of bytes. - - ----------------- Format Atom (12 bytes) -------------------------------- -(uint_32) Format Atom Size // = 12 -(uint_32) Channel Layout Info ID // = 'frma' -(uint_32) Format Type // = 'alac' - ----------------- ALAC Specific Info (36 bytes) (required) -------------- -(uint_32) ALAC Specific Info Size // = 36 (12 + sizeof(ALACSpecificConfig)) -(uint_32) ALAC Specific Info ID // = 'alac', format ID which matches the Audio Sample Entry SampleEntryType field -(uint_32) Version Flags // = 0 - - [ Apple Lossless Magic Cookie (see above) ] - ----------------- Terminator Atom (8 bytes) ----------------------------- -(uint_32) Channel Layout Info Size // = 8 -(uint_32) Channel Layout Info ID // = 0 - - -