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667 lines
31 KiB
667 lines
31 KiB
Encapsulation of FLAC in ISO Base Media File Format
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Version 0.0.4 (draft)
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Table of Contents
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1 Scope
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2 Supporting Normative References
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3 Design Rules of Encapsulation
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3.1 File Type Identification
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3.2 Overview of Track Structure
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3.3 Definition of FLAC sample
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3.3.1 Sample entry format
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3.3.2 FLAC Specific Box
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3.3.3 Sample format
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3.3.4 Duration of FLAC sample
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3.3.5 Sub-sample
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3.3.6 Random Access
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3.3.6.1 Random Access Point
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3.4 Basic Structure (informative)
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3.4.1 Initial Movie
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3.5 Example of Encapsulation (informative)
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4 Acknowledgements
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5 Author's Address
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1 Scope
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This document specifies the normative mapping for encapsulation of
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FLAC coded audio bitstreams in ISO Base Media file format and its
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derivatives. The encapsulation of FLAC coded bitstreams in
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QuickTime file format is outside the scope of this specification.
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2 Supporting Normative References
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[1] ISO/IEC 14496-12:2012 Corrected version
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Information technology — Coding of audio-visual objects — Part
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12: ISO base media file format
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[2] ISO/IEC 14496-12:2012/Amd.1:2013
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Information technology — Coding of audio-visual objects — Part
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12: ISO base media file format AMENDMENT 1: Various
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enhancements including support for large metadata
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[3] FLAC format specification
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https://xiph.org/flac/format.html
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Definition of the FLAC Audio Codec stream format
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[4] FLAC-in-Ogg mapping specification
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https://xiph.org/flac/ogg_mapping.html
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Ogg Encapsulation for the FLAC Audio Codec
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[5] Matroska specification
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3 Design Rules of Encapsulation
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3.1 File Type Identification
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This specification does not define any brand to declare files
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which conform to this specification. Files which conform to
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this specification shall contain at least one brand which
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supports the requirements and the requirements described in
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this clause without contradiction in the compatible brands
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list of the File Type Box. The minimal support of the
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encapsulation of FLAC bitstreams in ISO Base Media file format
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requires the 'isom' brand.
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3.2 Overview of Track Structure
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FLAC coded audio shall be encapsulated into the ISO Base
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Media File Format as media data within an audio track.
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+ The handler_type field in the Handler Reference Box
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shall be set to 'soun'.
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+ The Media Information Box shall contain the Sound Media
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Header Box.
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+ The codingname of the sample entry is 'fLaC'.
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This specification does not define any encapsulation
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using MP4AudioSampleEntry with objectTypeIndication
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specified by the MPEG-4 Registration Authority
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(http://www.mp4ra.org/). See section 'Sample entry
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format' for the definition of the sample entry.
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+ The 'dfLa' box is added to the sample entry to convey
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initializing information for the decoder.
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See section 'FLAC Specific Box' for the definition of
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the box contents.
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+ A FLAC sample is exactly one FLAC frame as described
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in the format specification[3]. See section
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'Sample format' for details of the frame contents.
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+ Every FLAC sample is a sync sample. No pre-roll or
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lapping is required. See section 'Random Access' for
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further details.
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3.3 Definition of a FLAC sample
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3.3.1 Sample entry format
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For any track containing one or more FLAC bitstreams, a
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sample entry describing the corresponding FLAC bitstream
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shall be present inside the Sample Table Box. This version
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of the specification defines only one sample entry format
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named FLACSampleEntry whose codingname is 'fLaC'. This
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sample entry includes exactly one FLAC Specific Box
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defined in section 'FLAC specific box' as a mandatory box
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and indicates that FLAC samples described by this sample
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entry are stored by the sample format described in section
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'Sample format'.
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The syntax and semantics of the FLACSampleEntry is shown
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as follows. The data fields of this box and native
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FLAC[3] structures encoded within FLAC blocks are both
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stored in big-endian format, though for purposes of the
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ISO BMFF container, FLAC native metadata and data blocks
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are treated as unstructured octet streams.
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class FLACSampleEntry() extends AudioSampleEntry ('fLaC'){
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FLACSpecificBox();
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}
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The fields of the AudioSampleEntry portion shall be set as
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follows:
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+ channelcount:
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The channelcount field shall be set equal to the
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channel count specified by the FLAC bitstream's native
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METADATA_BLOCK_STREAMINFO header as described in [3].
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Note that the FLAC FRAME_HEADER structure that begins
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each FLAC sample redundantly encodes channel number;
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the number of channels declared in each FRAME_HEADER
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MUST match the number of channels declared here and in
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the METADATA_BLOCK_STREAMINFO header.
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+ samplesize:
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The samplesize field shall be set equal to the bits
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per sample specified by the FLAC bitstream's native
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METADATA_BLOCK_STREAMINFO header as described in [3].
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Note that the FLAC FRAME_HEADER structure that begins
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each FLAC sample redundantly encodes the number of
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bits per sample; the bits per sample declared in each
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FRAME_HEADER MUST match the samplesize declared here
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and the bits per sample field declared in the
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METADATA_BLOCK_STREAMINFO header.
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+ samplerate:
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When possible, the samplerate field shall be set
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equal to the sample rate specified by the FLAC
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bitstream's native METADATA_BLOCK_STREAMINFO header
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as described in [3], left-shifted by 16 bits to
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create the appropriate 16.16 fixed-point
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representation.
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When the bitstream's native sample rate is greater
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than the maximum expressible value of 65535 Hz,
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the samplerate field shall hold the greatest
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expressible regular division of that rate. I.e.
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the samplerate field shall hold 48000.0 for
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native sample rates of 96 and 192 kHz. In the
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case of unusual sample rates which do not have
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an expressible regular division, the maximum value
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of 65535.0 Hz should be used.
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High-rate FLAC bitstreams are common, and the native
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value from the METADATA_BLOCK_STREAMINFO header in
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the FLACSpecificBox MUST be read to determine the
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correct sample rate of the bitstream.
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Note that the FLAC FRAME_HEADER structure that begins
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each FLAC sample redundantly encodes the sample rate;
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the sample rate declared in each FRAME_HEADER MUST
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match the sample rate declared in the
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METADATA_BLOCK_STREAMINFO header, and here in the
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AudioSampleEntry portion of the FLACSampleEntry
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as much as is allowed by the encoding restrictions
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described above.
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Finally, the FLACSpecificBox carries codec headers:
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+ FLACSpecificBox
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This box contains initializing information for the
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decoder as defined in section 'FLAC specific box'.
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3.3.2 FLAC Specific Box
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Exactly one FLAC Specific Box shall be present in each
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FLACSampleEntry. This specification defines version 0
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of this box. If incompatible changes occur in future
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versions of this specification, another version number
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will be defined. The data fields of this box and native
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FLAC[3] structures encoded within FLAC blocks are both
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stored in big-endian format, though for purposes of the
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ISO BMFF container, FLAC native metadata and data blocks
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are treated as unstructured octet streams.
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The syntax and semantics of the FLAC Specific Box is shown
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as follows.
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class FLACMetadataBlock {
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unsigned int(1) LastMetadataBlockFlag;
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unsigned int(7) BlockType;
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unsigned int(24) Length;
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unsigned int(8) BlockData[Length];
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}
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aligned(8) class FLACSpecificBox
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extends FullBox('dfLa', version=0, 0){
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for (i=0; ; i++) { // to end of box
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FLACMetadataBlock();
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}
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}
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+ Version:
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The Version field shall be set to 0.
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In the future versions of this specification, this
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field may be set to other values. And without support
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of those values, the reader shall not read the fields
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after this within the FLACSpecificBox.
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+ Flags:
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The Flags field shall be set to 0.
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After the FullBox header, the box contains a sequence of
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FLAC[3] native-metadata block structures that fill the
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remainder of the box.
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Each FLACMetadataBlock structure consists of three fields
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filling a total of four bytes that form a FLAC[3] native
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METADATA_BLOCK_HEADER, followed by raw octet bytes that
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comprise the FLAC[3] native METADATA_BLOCK_DATA.
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+ LastMetadataBlockFlag:
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The LastMetadataBlockFlag field maps semantically to
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the FLAC[3] native METADATA_BLOCK_HEADER
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Last-metadata-block flag as defined in the FLAC[3]
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file specification.
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The LastMetadataBlockFlag is set to 1 if this
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MetadataBlock is the last metadata block in the
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FLACSpecificBox. It is set to 0 otherwise.
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+ BlockType:
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The BlockType field maps semantically to the FLAC[3]
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native METADATA_BLOCK_HEADER BLOCK_TYPE field as
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defined in the FLAC[3] file specification.
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The BlockType is set to a valid FLAC[3] BLOCK_TYPE
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value that identifies the type of this native metadata
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block. The BlockType of the first FLACMetadataBlock
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must be set to 0, signifying this is a FLAC[3] native
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METADATA_BLOCK_STREAMINFO block.
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+ Length:
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The Length field maps semantically to the FLAC[3]
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native METADATA_BLOCK_HEADER Length field as
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defined in the FLAC[3] file specification.
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The length field specifies the number of bytes of
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MetadataBlockData to follow.
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+ BlockData
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The BlockData field maps semantically to the FLAC[3]
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native METADATA_BLOCK_HEADER METADATA_BLOCK_DATA as
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defined in the FLAC[3] file specification.
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Taken together, the bytes of the FLACMetadataBlock form a
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complete FLAC[3] native METADATA_BLOCK structure.
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Note that a minimum of a single FLACMetadataBlock,
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consisting of a FLAC[3] native METADATA_BLOCK_STREAMINFO
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structure, is required. Should the FLACSpecificBox
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contain more than a single FLACMetadataBlock structure,
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the FLACMetadataBlock containing the FLAC[3] native
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METADATA_BLOCK_STREAMINFO must occur first in the list.
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Other containers that package FLAC audio streams, such as
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Ogg[4] and Matroska[5], wrap FLAC[3] native metadata without
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modification similar to this specification. When
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repackaging or remuxing FLAC[3] streams from another
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format that contains FLAC[3] native metadata into an ISO
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BMFF file, the complete FLAC[3] native metadata should be
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preserved in the ISO BMFF stream as described above. It
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is also allowed to parse this native metadata and include
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contextually redundant ISO BMFF-native repackagings and/or
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reparsings of FLAC[3] native metadata, so long as the
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native metadata is also preserved.
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3.3.3 Sample format
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A FLAC sample is exactly one FLAC audio FRAME (as defined
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in the FLAC[3] file specification) belonging to a FLAC
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bitstreams. The FLAC sample data begins with a complete
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FLAC FRAME_HEADER, followed by one FLAC SUBFRAME per
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channel, any necessary bit padding, and ends with the
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usual FLAC FRAME_FOOTER.
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Note that the FLAC native FRAME_HEADER structure that
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begins each FLAC sample redundantly encodes channel count,
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sample rate, and sample size. The values of these fields
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must agree both with the values declared in the FLAC
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METADATA_BLOCK_STREAMINFO structure as well as the
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FLACSampleEntry box.
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3.3.4 Duration of a FLAC sample
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The duration of any given FLAC sample is determined by
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dividing the decoded block size of a FLAC frame, as
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encoded in the FLAC FRAME's FRAME_HEADER structure, by the
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value of the timescale field in the Media Header Box.
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FLAC samples are permitted to have variable durations
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within a given audio stream. FLAC does not use padding
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values.
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3.3.5 Sub-sample
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Sub-samples are not defined for FLAC samples in this
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specification.
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3.3.6 Random Access
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This subclause describes the nature of the random access
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of FLAC sample.
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3.3.6.1 Random Access Point
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All FLAC samples can be independently decoded
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i.e. every FLAC sample is a sync sample. The Sync
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Sample Box shall not be present as long as there are
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no samples other than FLAC samples in the same
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track. The sample_is_non_sync_sample field for FLAC
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samples shall be set to 0.
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3.4 Basic Structure (informative)
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3.4.1 Initial Movie
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This subclause shows a basic structure of the Movie Box as follows:
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+----+----+----+----+----+----+----+----+------------------------------+
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|moov| | | | | | | | Movie Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| |mvhd| | | | | | | Movie Header Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| |trak| | | | | | | Track Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | |tkhd| | | | | | Track Header Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | |edts|* | | | | | Edit Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | |elst|* | | | | Edit List Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | |mdia| | | | | | Media Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | |mdhd| | | | | Media Header Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | |hdlr| | | | | Handler Reference Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | |minf| | | | | Media Information Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | |smhd| | | | Sound Media Header Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | |dinf| | | | Data Information Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | |dref| | | Data Reference Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | | |url | | DataEntryUrlBox |
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+----+----+----+----+----+----+ or +----+------------------------------+
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| | | | | | |urn | | DataEntryUrnBox |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | |stbl| | | | Sample Table |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | |stsd| | | Sample Description Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | | |fLaC| | FLACSampleEntry |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | | | |dfLa| FLAC Specific Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | |stts| | | Decoding Time to Sample Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | |stsc| | | Sample To Chunk Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | |stsz| | | Sample Size Box |
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+----+----+----+----+----+ or +----+----+------------------------------+
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| | | | | |stz2| | | Compact Sample Size Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | | | | |stco| | | Chunk Offset Box |
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+----+----+----+----+----+ or +----+----+------------------------------+
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| | | | | |co64| | | Chunk Large Offset Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| |mvex|* | | | | | | Movie Extends Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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| | |trex|* | | | | | Track Extends Box |
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+----+----+----+----+----+----+----+----+------------------------------+
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Figure 1 - Basic structure of Movie Box
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It is strongly recommended that the order of boxes should
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follow the above structure. Boxes marked with an asterisk
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(*) may or may not be present depending on context. For
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most boxes listed above, the definition is as is defined
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in ISO/IEC 14496-12 [1]. The additional boxes and the
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additional requirements, restrictions and recommendations
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to the other boxes are described in this specification.
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3.5 Example of Encapsulation (informative)
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[File]
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size = 17790
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[ftyp: File Type Box]
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position = 0
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size = 24
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major_brand = mp42 : MP4 version 2
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minor_version = 0
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compatible_brands
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brand[0] = mp42 : MP4 version 2
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brand[1] = isom : ISO Base Media file format
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[moov: Movie Box]
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position = 24
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size = 757
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[mvhd: Movie Header Box]
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position = 32
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size = 108
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version = 0
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flags = 0x000000
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creation_time = UTC 2014/12/12, 18:41:19
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modification_time = UTC 2014/12/12, 18:41:19
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timescale = 48000
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duration = 33600 (00:00:00.700)
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rate = 1.000000
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volume = 1.000000
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reserved = 0x0000
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reserved = 0x00000000
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reserved = 0x00000000
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transformation matrix
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| a, b, u | | 1.000000, 0.000000, 0.000000 |
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| c, d, v | = | 0.000000, 1.000000, 0.000000 |
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| x, y, w | | 0.000000, 0.000000, 1.000000 |
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pre_defined = 0x00000000
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pre_defined = 0x00000000
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pre_defined = 0x00000000
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pre_defined = 0x00000000
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pre_defined = 0x00000000
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pre_defined = 0x00000000
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next_track_ID = 2
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[iods: Object Descriptor Box]
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position = 140
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size = 33
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version = 0
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flags = 0x000000
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[tag = 0x10: MP4_IOD]
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expandableClassSize = 16
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ObjectDescriptorID = 1
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URL_Flag = 0
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includeInlineProfileLevelFlag = 0
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reserved = 0xf
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ODProfileLevelIndication = 0xff
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sceneProfileLevelIndication = 0xff
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audioProfileLevelIndication = 0xfe
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visualProfileLevelIndication = 0xff
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graphicsProfileLevelIndication = 0xff
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[tag = 0x0e: ES_ID_Inc]
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expandableClassSize = 4
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Track_ID = 1
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[trak: Track Box]
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position = 173
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size = 608
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[tkhd: Track Header Box]
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position = 181
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size = 92
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version = 0
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flags = 0x000007
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Track enabled
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Track in movie
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Track in preview
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creation_time = UTC 2014/12/12, 18:41:19
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modification_time = UTC 2014/12/12, 18:41:19
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track_ID = 1
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reserved = 0x00000000
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duration = 33600 (00:00:00.700)
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reserved = 0x00000000
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reserved = 0x00000000
|
|
layer = 0
|
|
alternate_group = 0
|
|
volume = 1.000000
|
|
reserved = 0x0000
|
|
transformation matrix
|
|
| a, b, u | | 1.000000, 0.000000, 0.000000 |
|
|
| c, d, v | = | 0.000000, 1.000000, 0.000000 |
|
|
| x, y, w | | 0.000000, 0.000000, 1.000000 |
|
|
width = 0.000000
|
|
height = 0.000000
|
|
[mdia: Media Box]
|
|
position = 273
|
|
size = 472
|
|
[mdhd: Media Header Box]
|
|
position = 281
|
|
size = 32
|
|
version = 0
|
|
flags = 0x000000
|
|
creation_time = UTC 2014/12/12, 18:41:19
|
|
modification_time = UTC 2014/12/12, 18:41:19
|
|
timescale = 48000
|
|
duration = 34560 (00:00:00.720)
|
|
language = und
|
|
pre_defined = 0x0000
|
|
[hdlr: Handler Reference Box]
|
|
position = 313
|
|
size = 51
|
|
version = 0
|
|
flags = 0x000000
|
|
pre_defined = 0x00000000
|
|
handler_type = soun
|
|
reserved = 0x00000000
|
|
reserved = 0x00000000
|
|
reserved = 0x00000000
|
|
name = Xiph Audio Handler
|
|
[minf: Media Information Box]
|
|
position = 364
|
|
size = 381
|
|
[smhd: Sound Media Header Box]
|
|
position = 372
|
|
size = 16
|
|
version = 0
|
|
flags = 0x000000
|
|
balance = 0.000000
|
|
reserved = 0x0000
|
|
[dinf: Data Information Box]
|
|
position = 388
|
|
size = 36
|
|
[dref: Data Reference Box]
|
|
position = 396
|
|
size = 28
|
|
version = 0
|
|
flags = 0x000000
|
|
entry_count = 1
|
|
[url : Data Entry Url Box]
|
|
position = 412
|
|
size = 12
|
|
version = 0
|
|
flags = 0x000001
|
|
location = in the same file
|
|
[stbl: Sample Table Box]
|
|
position = 424
|
|
size = 321
|
|
[stsd: Sample Description Box]
|
|
position = 432
|
|
size = 79
|
|
version = 0
|
|
flags = 0x000000
|
|
entry_count = 1
|
|
[fLaC: Audio Description]
|
|
position = 448
|
|
size = 63
|
|
reserved = 0x000000000000
|
|
data_reference_index = 1
|
|
reserved = 0x0000
|
|
reserved = 0x0000
|
|
reserved = 0x00000000
|
|
channelcount = 2
|
|
samplesize = 16
|
|
pre_defined = 0
|
|
reserved = 0
|
|
samplerate = 48000.000000
|
|
[dfLa: FLAC Specific Box]
|
|
position = 484
|
|
size = 50
|
|
version = 0
|
|
flags = 0x000000
|
|
[FLACMetadataBlock]
|
|
LastMetadataBlockFlag = 1
|
|
BlockType = 0
|
|
Length = 34
|
|
BlockData[34];
|
|
[stts: Decoding Time to Sample Box]
|
|
position = 492
|
|
size = 24
|
|
version = 0
|
|
flags = 0x000000
|
|
entry_count = 1
|
|
entry[0]
|
|
sample_count = 18
|
|
sample_delta = 1920
|
|
[stsc: Sample To Chunk Box]
|
|
position = 516
|
|
size = 40
|
|
version = 0
|
|
flags = 0x000000
|
|
entry_count = 2
|
|
entry[0]
|
|
first_chunk = 1
|
|
samples_per_chunk = 13
|
|
sample_description_index = 1
|
|
entry[1]
|
|
first_chunk = 2
|
|
samples_per_chunk = 5
|
|
sample_description_index = 1
|
|
[stsz: Sample Size Box]
|
|
position = 556
|
|
size = 92
|
|
version = 0
|
|
flags = 0x000000
|
|
sample_size = 0 (variable)
|
|
sample_count = 18
|
|
entry_size[0] = 977
|
|
entry_size[1] = 938
|
|
entry_size[2] = 939
|
|
entry_size[3] = 938
|
|
entry_size[4] = 934
|
|
entry_size[5] = 945
|
|
entry_size[6] = 948
|
|
entry_size[7] = 956
|
|
entry_size[8] = 955
|
|
entry_size[9] = 930
|
|
entry_size[10] = 933
|
|
entry_size[11] = 934
|
|
entry_size[12] = 972
|
|
entry_size[13] = 977
|
|
entry_size[14] = 958
|
|
entry_size[15] = 949
|
|
entry_size[16] = 962
|
|
entry_size[17] = 848
|
|
[stco: Chunk Offset Box]
|
|
position = 648
|
|
size = 24
|
|
version = 0
|
|
flags = 0x000000
|
|
entry_count = 2
|
|
chunk_offset[0] = 686
|
|
chunk_offset[1] = 12985
|
|
[free: Free Space Box]
|
|
position = 672
|
|
size = 8
|
|
[mdat: Media Data Box]
|
|
position = 680
|
|
size = 17001
|
|
|
|
4 Acknowledgements
|
|
|
|
This spec draws heavily from the Opus-in-ISOBMFF specification
|
|
work done by Yusuke Nakamura <muken.the.vfrmaniac |at| gmail.com>
|
|
|
|
Thank you to Tim Terriberry, David Evans, and Yusuke Nakamura
|
|
for valuable feedback. Thank you to Ralph Giles for editorial
|
|
help.
|
|
|
|
5 Author Address
|
|
|
|
Monty Montgomery <cmontgomery@mozilla.com>
|