Commit 2fd3c22f authored by Ralph Giles's avatar Ralph Giles Committed by Erik de Castro Lopo
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Flac-in-mp4 draft v0.0.2.



Draft updates in response to feedback from David Evans.
Signed-off-by: Erik de Castro Lopo's avatarErik de Castro Lopo <erikd@mega-nerd.com>
parent 52df9c61
Encapsulation of FLAC in ISO Base Media File Format
Version 0.0.1 (draft)
Version 0.0.2 (draft)
Table of Contents
1 Scope
2 Supproting Normative References
2 Supporting Normative References
3 Terms and Definitions
4 Design Rules of Encapsulation
4.1 File Type Indentification
4.1 File Type Identification
4.2 Overview of Track Structure
4.3 Definition of FLAC sample
4.3.1 Sample entry format
......@@ -46,13 +46,13 @@ Table of Contents
https://xiph.org/flac/format.html
Definition of the FLAC Audio Codec stream format
Definition of the FLAC Audio Codec stream format
[4] FLAC-in-Ogg mapping specification
https://xiph.org/flac/ogg_mapping.html
https://xiph.org/flac/ogg_mapping.html
Ogg Encapsulation for the FLAC Audio Codec
Ogg Encapsulation for the FLAC Audio Codec
[5] Matroska specification
......@@ -75,45 +75,46 @@ Table of Contents
4 Design Rules of Encapsulation
4.1 File Type Indentification
4.1 File Type Identification
This specification does not define any brand to declare files
are conformant to this specification. Files conformant to
which conform to this specification. Files which conform to
this specification shall contain at least one brand which
supports the requirements and the requirements described in
this clause without contradiction in the compatible brands
list of the File Type Box. The minimal support of the
encapsulation of FLAC bitstreams in ISO Base Media file format
requires the 'isom' brand.
4.2 Overview of Track Structure
FLAC coded audio shall be encapsulated into the ISO Base
Media File Format as media data within an audio track.
+ The handler_type field in the Handler Reference Box
shall be set to 'soun'.
+ The Media Information Box shall contain the Sound Media
Header Box.
+ The codingname of the sample entry is 'fLaC'.
This specification does not define any encapsulation
using MP4AudioSampleEntry with objectTypeIndication
specified by the MPEG-4 Registration Authority
(http://www.mp4ra.org/). See section 'Sample entry
format' for the definition of the the sample entry.
format' for the definition of the sample entry.
+ The 'dfLa' box is added to the sample entry to convey
initializing information for the decoder.
See section 'FLAC Specific Box' for the definition of
See section 'FLAC Specific Box' for the definition of
the box contents.
+ A FLAC sample is exactly one FLAC packet. See section
'Sample format' for details of the packet contents.
+ A FLAC sample is exactly one FLAC frame as described
in the format specification[3]. See section
'Sample format' for details of the frame contents.
+ Every FLAC sample is a sync sample. No pre-roll or
lapping is required. See section 'Random Access' for
further details.
......@@ -122,11 +123,11 @@ Table of Contents
4.3.1 Sample entry format
For any track containing one or more FLAC bitstreams, a
For any track containing one or more FLAC bitstreams, a
sample entry describing the corresponding FLAC bitstream
shall be present inside the Sample Table Box. This version
of the specification defines only one sample entry format
named FLACSampleEntry whose codingname is 'fLaC'. This
named FLACSampleEntry whose codingname is 'fLaC'. This
sample entry includes exactly one FLAC Specific Box
defined in section 'FLAC specific box' as a mandatory box
and indicates that FLAC samples described by this sample
......@@ -139,34 +140,37 @@ Table of Contents
stored in big-endian format, though for purposes of the
ISO BMFF container, FLAC native metadata and data blocks
are treated as unstructured octet streams.
class FLACSampleEntry() extends AudioSampleEntry ('fLaC'){
FLACSpecificBox();
}
The fields of the AudioSampleEntry portion shall be set as
follows:
+ channelcount:
The channelcount field shall be set equal to the
channel count specified by the FLAC bitstream's native
METADATA_BLOCK_STREAMINFO header as described in [3].
Note that the FLAC FRAME_HEADER structure that begins
each FLAC sample redundantly encodes channel number;
the number of channels declared in each FRAME_HEADER
MUST match the number of channels declared here and in
the METADATA_BLOCK_STREAMINFO header.
The channelcount field shall be set equal to the
channel count specified by the FLAC bitstream's native
METADATA_BLOCK_STREAMINFO header as described in [3].
Note that the FLAC FRAME_HEADER structure that begins
each FLAC sample redundantly encodes channel number;
the number of channels declared in each FRAME_HEADER
MUST match the number of channels declared here and in
the METADATA_BLOCK_STREAMINFO header.
+ samplesize:
The samplesize field shall be set equal to the bits
per sample specified by the FLAC bitstream's native
METADATA_BLOCK_STREAMINFO header as described in [3].
Note that the FLAC FRAME_HEADER structure that begins
each FLAC sample redundantly encodes the number of
bits per sample; the bits per sample declared in each
FRAME_HEADER MUST match the samplesize declared here
and the bits per sample field declared in the
METADATA_BLOCK_STREAMINFO header.
The samplesize field shall be set equal to the bits
per sample specified by the FLAC bitstream's native
METADATA_BLOCK_STREAMINFO header as described in [3].
Note that the FLAC FRAME_HEADER structure that begins
each FLAC sample redundantly encodes the number of
bits per sample; the bits per sample declared in each
FRAME_HEADER MUST match the samplesize declared here
and the bits per sample field declared in the
METADATA_BLOCK_STREAMINFO header.
+ samplerate:
The samplerate field shall be set equal to the sample
......@@ -178,14 +182,16 @@ Table of Contents
declared in each FRAME_HEADER MUST match the sample
rate declared here and in the
METADATA_BLOCK_STREAMINFO header.
Finally, the FLACSpecificBox carries codec headers:
+ FLACSpecificBox
This box contains initializing information for the
decoder as defined in section 'FLAC specific box'
4.3.2 FLAC Specific Box
Exactly one FLAC Specific Box shall be present in each
FLACSampleEntry. The FLAC Specific Box contains the
Version field and this specification defines version 0 of
......@@ -202,128 +208,120 @@ Table of Contents
as follows.
aligned(8) class FLACMetadataBlock {
unsigned int(1) LastMetadataBlockFlag;
unsigned int(7) BlockType;
unsigned int(24) Length;
unsigned int(8) MetadataBlockData[BlockLength];
unsigned int(1) LastMetadataBlockFlag;
unsigned int(7) BlockType;
unsigned int(24) Length;
unsigned int(8) BlockData[Length];
}
aligned(8) class FLACSpecificBox
(unsigned int32 MetadataBlocks) extends Box('dfLa'){
unsigned int(8) Version;
for(i=0; i <= MetadataBlocks; i++){
FLACMetadataBlock();
}
aligned(8) class FLACSpecificBox
extends FullBox('dfLa', version=0, 0){
for (i=0; ; i++) { // to end of box
FLACMetadataBlock();
}
}
+ MetadataBlocks:
The number of FLAC[3] native metadata blocks to
follow. This value must be at least 1 as a native
METADATA_BLOCK_STREAMINFO structure is required to
decode FLAC audio data.
This value is not coded as the end of the
FLACMetadataBlock list can be intuited from the
LastMetadataBlockFlag (see below).
+ Version:
The Version field shall be set to 0.
The Version field shall be set to 0.
In the future versions of this specification, this
In the future versions of this specification, this
field may be set to other values. And without support
of those values, the reader shall not read the fields
after this within the FLACSpecificBox.
The Version field is followed by a sequence of FLAC[3]
native-metadata block structures that fill the remainder
of the box length.
+ LastMetadataBlockFlag:
The LastMetadataBlockFlag field maps semantically to
the FLAC[3] native MEATADATA_BLOCK_HEADER
Last-metadata-block flag as defined in the FLAC[3]
file specification.
The LastMetadataBlockFlag is set to 1 if this
MetadataBlock is the last metadata block in the
FLACSpecificBox. It is set to 0 otherwise.
+ BlockType:
The BlockType field maps semantically to the FLAC[3]
native MEATADATA_BLOCK_HEADER BLOCK_TYPE field as
defined in the FLAC[3] file specification.
The BlockType is set to a valid FLAC[3] BLOCK_TYPE
value that identifies the type of this native metadata
block. The BlockType of the first FLACMetadataBlock
must be set to 0, signifying this is a FLAC[3] native
METADATA_BLOCK_STREAMINFO block.
+ Length:
The Length field maps semantically to the FLAC[3]
native MEATADATA_BLOCK_HEADER Length field as
defined in the FLAC[3] file specification.
The length field specifies the number of bytes of
MetadataBlockData to follow.
+ MetadataBlockData
The MetadataBlockData field maps semantically to the
FLAC[3] native MEATADATA_BLOCK_HEADER
METADATA_BLOCKDATA as defined in the FLAC[3] file
specification.
The FLACMetadataBlock structure consists of three fields
filling a total of four bytes that form a FLAC[3] native
METADATA_BLOCK_HEADER, followed by raw octet bytes that
comprise the FLAC[3] native METADATA_BLOCK_DATA. Taken
together, the bytes of the FLACMetadataBlock form a
complete FLAC[3] native METADATA_BLOCK structure.
Note that a minimum of a single FLACMetadataBlock,
consisting of a FLAC[3] native METADATA_BLOCK_STREAMINFO
structure, is required. Should the FLACSpecificBox
contain more than a single FLACMetadataBlock structure,
the FLACMetadataBlock contianing the FLAC[3] native
METADATA_BLOCK_STREAMINFO must occur first in the list.
Other containers that package FLAC audio streams, such as
Ogg[4] and Matroska[5], wrap FLAC[3] native metadata without
modification similar to this specification. When
repackaging or remuxing FLAC[3] streams from another
format that contains FLAC[3] native metadata into an ISO
BMFF file, the complete FLAC[3] native metadata should be
preserved in the ISO BMFF stream as described above. It
is also allowed to parse this native metadata and include
contextually redundant ISO BMFF-native repackagings and/or
reparsings of FLAC[3] native metadata, so long as the
native metadata is also preserved.
+ Flags:
The Flags field shall be set to 0.
After the FullBox header, the box contains a sequence of
FLAC[3] native-metadata block structures that fill the
remainder of the box.
Each FLACMetadataBlock structure consists of three fields
filling a total of four bytes that form a FLAC[3] native
METADATA_BLOCK_HEADER, followed by raw octet bytes that
comprise the FLAC[3] native METADATA_BLOCK_DATA.
+ LastMetadataBlockFlag:
The LastMetadataBlockFlag field maps semantically to
the FLAC[3] native METADATA_BLOCK_HEADER
Last-metadata-block flag as defined in the FLAC[3]
file specification.
The LastMetadataBlockFlag is set to 1 if this
MetadataBlock is the last metadata block in the
FLACSpecificBox. It is set to 0 otherwise.
+ BlockType:
The BlockType field maps semantically to the FLAC[3]
native MEATADATA_BLOCK_HEADER BLOCK_TYPE field as
defined in the FLAC[3] file specification.
The BlockType is set to a valid FLAC[3] BLOCK_TYPE
value that identifies the type of this native metadata
block. The BlockType of the first FLACMetadataBlock
must be set to 0, signifying this is a FLAC[3] native
METADATA_BLOCK_STREAMINFO block.
+ Length:
The Length field maps semantically to the FLAC[3]
native MEATADATA_BLOCK_HEADER Length field as
defined in the FLAC[3] file specification.
The length field specifies the number of bytes of
MetadataBlockData to follow.
+ BlockData
The BlockData field maps semantically to the FLAC[3]
native MEATADATA_BLOCK_HEADER METADATA_BLOCK_DATA as
defined in the FLAC[3] file specification.
Taken together, the bytes of the FLACMetadataBlock form a
complete FLAC[3] native METADATA_BLOCK structure.
Note that a minimum of a single FLACMetadataBlock,
consisting of a FLAC[3] native METADATA_BLOCK_STREAMINFO
structure, is required. Should the FLACSpecificBox
contain more than a single FLACMetadataBlock structure,
the FLACMetadataBlock containing the FLAC[3] native
METADATA_BLOCK_STREAMINFO must occur first in the list.
Other containers that package FLAC audio streams, such as
Ogg[4] and Matroska[5], wrap FLAC[3] native metadata without
modification similar to this specification. When
repackaging or remuxing FLAC[3] streams from another
format that contains FLAC[3] native metadata into an ISO
BMFF file, the complete FLAC[3] native metadata should be
preserved in the ISO BMFF stream as described above. It
is also allowed to parse this native metadata and include
contextually redundant ISO BMFF-native repackagings and/or
reparsings of FLAC[3] native metadata, so long as the
native metadata is also preserved.
4.3.3 Sample format
A FLAC sample is exactly one FLAC audio FRAME packet (as
defined in the FLAC[3] file specification) belonging to a
FLAC bitstreams. The FLAC sample data begins with a
complete FLAC FRAME_HEADER, followed by one FLAC SUBFRAME
per channel, any necessary bit padding, and ends with the
A FLAC sample is exactly one FLAC audio FRAME (as defined
in the FLAC[3] file specification) belonging to a FLAC
bitstreams. The FLAC sample data begins with a complete
FLAC FRAME_HEADER, followed by one FLAC SUBFRAME per
channel, any necessary bit padding, and ends with the
usual FLAC FRAME_FOOTER.
Note that the FLAC native FRAME_HEADER structure that
begins each FLAC sample redundantly encodes channel count,
sample rate, and sample size. The values of these fields
must agree both with the values declared in the FLAC
METADATA_BLOCK_STREAMINFO structure as well as the
FLACDSampleEntry box.
Note that the FLAC native FRAME_HEADER structure that
begins each FLAC sample redundantly encodes channel count,
sample rate, and sample size. The values of these fields
must agree both with the values declared in the FLAC
METADATA_BLOCK_STREAMINFO structure as well as the
FLACSampleEntry box.
4.3.4 Duration of a FLAC sample
The duration of any given FLAC sample is determined by
The duration of any given FLAC sample is determined by
dividing the decoded block size of a FLAC frame, as
encoded in the FLAC FRAME's FRAME_HEADER structure, by the
value of the timescale field in the Media Header Box.
......@@ -337,11 +335,11 @@ Table of Contents
specification.
4.3.6 Random Access
This subclause describes the nature of the random access of FLAC sample.
4.3.6.1 Random Access Point
All FLAC samples can be independently decoded
i.e. every FLAC sample is a sync sample. The Sync
Sample Box shall not be present as long as there are
......@@ -352,7 +350,7 @@ Table of Contents
4.4 Basic Structure (informative)
4.4.1 Initial Movie
This subclause shows a basic structure of the Movie Box as follows:
+----+----+----+----+----+----+----+----+------------------------------+
......@@ -420,7 +418,7 @@ Table of Contents
in ISO/IEC 14496-12 [1]. The additional boxes and the
additional requirements, restrictions and recommendations
to the other boxes are described in this specification.
4.5 Example of Encapsulation (informative)
[File]
size = 17790
......@@ -581,15 +579,16 @@ Table of Contents
samplerate = 48000.000000
[dfLa: FLAC Specific Box]
position = 484
size = 48
Version = 0
MetadataBlocks = 1
LastMetadataBlockFlag = 1
BlockType = 0
Length = 34
MetadataBlockData[34];
size = 50
version = 0
flags = 0x000000
[FLACMetaDataBlock]
LastMetadataBlockFlag = 1
BlockType = 0
Length = 34
BlockData[34];
[stts: Decoding Time to Sample Box]
position = 490
position = 492
size = 24
version = 0
flags = 0x000000
......@@ -598,7 +597,7 @@ Table of Contents
sample_count = 18
sample_delta = 1920
[stsc: Sample To Chunk Box]
position = 514
position = 516
size = 40
version = 0
flags = 0x000000
......@@ -612,7 +611,7 @@ Table of Contents
samples_per_chunk = 5
sample_description_index = 1
[stsz: Sample Size Box]
position = 554
position = 556
size = 92
version = 0
flags = 0x000000
......@@ -637,7 +636,7 @@ Table of Contents
entry_size[16] = 962
entry_size[17] = 848
[stco: Chunk Offset Box]
position = 646
position = 648
size = 24
version = 0
flags = 0x000000
......@@ -645,10 +644,10 @@ Table of Contents
chunk_offset[0] = 686
chunk_offset[1] = 12985
[free: Free Space Box]
position = 670
position = 672
size = 8
[mdat: Media Data Box]
position = 678
position = 680
size = 17001
5 Acknowledgements
......
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