From de579036bf52fe6560c4f3b43a35e6097e4d7859 Mon Sep 17 00:00:00 2001
From: Thomas Heritage <thomas.heritage@bbc.co.uk>
Date: Fri, 8 Dec 2023 10:03:15 +0000
Subject: [PATCH] Update documentation re ADM-related features

* Fix some typos
* Re-word for clarity
* Update to match latest functionality
* :question: is used in some areas requiring confirmation
---
 README.md                      |   2 +-
 apps/raw2bmx/raw2bmx.cpp       |   2 +-
 docs/audio_definition_model.md | 192 +++++++++++++++++++++------------
 docs/mca_labels_format.md      |  26 +++--
 4 files changed, 139 insertions(+), 83 deletions(-)

diff --git a/README.md b/README.md
index 34a58e72..3ae024b5 100644
--- a/README.md
+++ b/README.md
@@ -64,7 +64,7 @@ including the following:
     * [IMF JPEG 2000 Track Files](./docs/imf_jpeg_2000_track_files.md)
     * [IMF Audio Track Files](./docs/imf_audio_track_files.md)
     * [IMF ProRes Image Track Files](./docs/imf_prores_track_files.md)
-* [Audio Definition Model](./docs/audio_definition_model.md)
+* [(Beta) Audio Definition Model (ADM) & metadata RIFF chunks](./docs/audio_definition_model.md)
 
 ## Build, Test and Install
 
diff --git a/apps/raw2bmx/raw2bmx.cpp b/apps/raw2bmx/raw2bmx.cpp
index 3c8b2a35..10fde847 100644
--- a/apps/raw2bmx/raw2bmx.cpp
+++ b/apps/raw2bmx/raw2bmx.cpp
@@ -720,7 +720,7 @@ static void usage(const char *cmd)
     printf("  --wave-chunks <ids>                List of non-builtin WAVE chunk IDs to transfer across from the input\n");
     printf("                                     The <ids> is a comma separated list of chunk IDs. Spaces are automatically appended to IDs if they are less than 4 letters\n");
     printf("                                     The built-in WAVE chunk IDs are: %s\n", WaveReader::GetBuiltinChunkListString().c_str());
-    printf("  --adm-wave-chunk <id>[,<label>]*   Identifies a npn-builtin ADM WAVE chunk to transfer across from the input\n");
+    printf("  --adm-wave-chunk <id>[,<label>]*   Identifies a non-builtin ADM WAVE chunk to transfer across from the input\n");
     printf("                                     ADM Soundfield Groups can be reference this chunk\n");
     printf("                                     A comma separated list of profile and level labels can be provided as well. A <label> can be:\n");
     printf("                                       * a SMPTE UL, formatted as a 'urn:smpte:ul:...',\n");
diff --git a/docs/audio_definition_model.md b/docs/audio_definition_model.md
index 8bb9e25f..5f9edb30 100644
--- a/docs/audio_definition_model.md
+++ b/docs/audio_definition_model.md
@@ -1,42 +1,84 @@
-# Audio Definition Model (ADM) Support
+# (BETA) -- Audio Definition Model (ADM) and other audio metadata RIFF Chunks
 
-A SMPTE project named "31FS ST Mapping ADM to MXF" started in March 2022 to "define a means of mapping audio metadata RIFF chunks to MXF with specific consideration of the requirements related to ADM metadata (for example, with reference to ADM carriage in BW64 files per Rec. ITU-R BS.2088-1)."
+## Quick start: Example: convert Wave+ADM (BW64) to IMF ADM Audio Track File (MXF)
 
-Provisional support for ADM has been implemented in `bmx` to allow samples files to be created to support the SMPTE project. The current level of support in the `bmx` implementation is as follows:
+Input: `wav_adm.wav` -- BW64 Wave file containing audio data, a \<chna\> chunk, and ADM XML metadata in an \<axml\> chunk
 
-- Reading Wave (BW64) with access to Wave chunks (e.g. ADM \<axml\>) and a parsed ADM \<chna\> chunk
-- Writing Wave (BW64) with additional Wave chunks (e.g. ADM \<axml\>) and a serialised ADM \<chna\> chunk
-- Reading MXF that includes Wave chunks and ADM \<chna\> descriptors
-- Writing MXF with Wave chunks and ADM \<chna\> descriptors
-- Converting Wave+ADM to MXF+ADM using raw2bmx
-- Converting Wave+ADM to Wave+ADM using raw2bmx
-- Converting MXF+ADM to Wave+ADM using bmxtranswrap
-- Creating Wave+ADM with Wave / raw PCM, \<chna\> text file and (optionally) Wave chunk file inputs (e.g. containing \<axml\> chunk data)
-- Preservation of ADM links after remapping audio channels using the `--track-map` option. The option can be used to reorder, omit, group and add silence channels.
-- Option to add a ADM Soundfield Group MCA label and identify ADM chunks
-- Set the Channel Assignment audio descriptor property for ADM-described content labelling
+Output: `adm_audio_track_file.mxf` -- an IMF ADM Audio Track File containing the same information, with all required MXF signalling added
 
-The known limitations in the current support are:
+The ADM XML metadata embedded in the Wave file:
+* defines two ADM audioProgramme entities
+* does not conform to any identified Profile or Level
 
-- mxf2raw doesn't yet show ADM metadata presence or allow ADM chunks or a \<chna\> text file to be extracted.
-- Re-wrapping a file using raw2bmx or bmxtranswrap with an offset or duration change may result in the ADM metadata and links becoming invalid. E.g. an audio object is no longer available in the new duration or the start offset has changed. The \<axml\>, \<bxml\> or \<sxml\> chunks are not parsed to ensure that the re-wrap retains valid ADM.
-- \> 4 GB chunk size is only supported for the data chunk. The ADM chunks are unlikely to be that large but it's worth adding support just in case that assumption is wrong.
+Example command:
+
+`raw2bmx -t imf -o adm_audio_track_file.mxf --audio-layout adm --track-mca-labels x mca.txt --adm-wave-chunk axml,adm_itu2076 --wave wav_adm.wav`
+
+where `mca.txt` contains:
+
+```text
+0
+ADM, chunk_id=axml, RFC5646SpokenLanguage="en-GB", MCATitle="Default", MCATitleVersion="n/a", MCAContent="PRM", MCAUseClass="FCMP", ADMAudioProgrammeID="APR_1001"
+ADM, chunk_id=axml, MCATitle="No Commentary", MCATitleVersion="n/a", MCAContent="PRM", MCAUseClass="FCMP", ADMAudioProgrammeID="APR_1002"
+```
+
+## SMPTE ST 2131 and SMPTE ST 2067-204
+
+SMPTE ST 2131 defines a mechanism for mapping Resource Interchange File Format (RIFF) Chunks containing audio metadata to MXF files to augment MXF Sound Tracks. It defines additional MXF support specifically for the mapping and labeling of content described by Audio Definition Model (ADM) metadata (Recommendation ITU-R BS.2076) which is often carried in Broadcast Wave 64-bit (BW64) RIFF files (Recommendation ITU-R BS.2088).
+
+SMPTE ST 2067-204 defines a plug-in mechanism to add audio with ADM metadata to IMF Compositions.
+
+Both documents are currently available as Public Committee Drafts (PCD):
+* https://github.com/SMPTE/st2131
+* https://github.com/SMPTE/st2067-204
+
+## bmx support
+
+Provisional support for SMPTE ST 2131 (PCD) has been implemented in `bmx`. This allows the creation of MXF files for a variety of use cases, including ADM Audio Track Files for use in IMF Compositions (per SMPTE ST 2067-204 (PCD)).
+
+The following formats are supported:
+* **Component form**
+  * Audio as Wave / raw PCM, \<chna\> text file (`bmx` format as [defined below](#chna-text-file-definition-format)) and Wave/RIFF chunk data files (e.g. ADM XML file)
+* **Wave (BW64)**
+  * Reading Wave (BW64) with access to Wave chunks (e.g. ADM \<axml\>) and a parsed ADM \<chna\> chunk
+  * Writing Wave (BW64) with additional Wave chunks (e.g. ADM \<axml\>) and a serialised ADM \<chna\> chunk
+* **MXF**
+  * Reading MXF that includes Wave chunks and ADM \<chna\> descriptors
+  * Writing MXF with Wave chunks and ADM \<chna\> descriptors
+  * Support for the ADMAudioMetadataSubDescriptor
+  * Support for the "Audio Labeling Framework for ADM-described Content" including the ADMSoundfieldGroupLabelSubDescriptor, the ADMSoundfield label, and signalling in the Channel Assignment audio descriptor property
+
+The I/O combinations supported by `bmx` tools are:
+
+|                   | Output (Component) | Output (Wave) | Output (MXF) |
+|-------------------|--------------------|---------------|--------------|
+| Input (Component) |                    | raw2bmx       |              |
+| Input (Wave)      |                    | raw2bmx       | raw2bmx      |
+| Input (MXF)       | mxf2raw            | bmxtranswrap  |              |
+
+Features:
+- Preservation of ADM references in the \<chna\> details after remapping audio channels using the `--track-map` option. The option can be used to reorder, omit, group and add silence channels.
+- The \<chna\> "summary" properties (numTracks and numUIDs in Wave files; NumLocalChannels and NumADMAudioTrackUIDs in MXF files) are discarded upon read of Wave/MXF files, and automatically calculated upon write of Wave/MXF files.
+
+The known limitations in the current implementation are:
+- mxf2raw doesn't yet show ADM metadata presence or extraction of all related signalling.
+- There is no parsing of the ADM metadata. Therefore, re-wrapping a file using raw2bmx or bmxtranswrap with an offset or duration change might result in the ADM metadata and references becoming invalid. For example, an ADM audio object might no longer be available after re-wrapping, or its start offset might have changed.
+- \> 4 GB chunk size is only supported for the \<data\> chunk. The ADM chunks are unlikely to be that large but ideally `bmx` would provide support.
 
 ## Wave+ADM to MXF+ADM mapping process
 
 The process of mapping Wave+ADM to MXF+ADM is basically as follows:
 
-- A \<chna\> chunk is converted to a ADM_CHNASubDescriptor descriptor in each track using the audio channel mapping defined by the `--track-map` option
-- The `--wave-chunks` and `--adm-wave-chunk` options are used to select the (non-builtin) chunks to transfer to the MXF file
-    - The builtin chunks that can't be selected are: \<JUNK\>, \<ds64\>, \<fmt\>, \<fact\>, \<bext\>, \<data\> and \<chna\>
+- A \<chna\> chunk is converted to a ADM_CHNASubDescriptor in each Sound Track using the audio channel mapping defined by the `--track-map` option
+    - Any null / placeholder entries (those with a trackIndex/track_index of zero) are discarded
+- The `--wave-chunks` and `--adm-wave-chunk` options are used to select the (non built-in) chunks to transfer to the MXF file
+    - The built-in chunks that can't be selected are: \<JUNK\>, \<ds64\>, \<fmt\>, \<fact\>, \<bext\>, \<data\> and \<chna\>
     - The chunk data is copied into MXF generic streams and each will have a RIFFChunkDefinitionSubDescriptor associated with it
-    - Audio tracks containing channels originating from the input file will reference all the chunks from that input file using RIFFChunkReferencesSubDescriptors
-- The `--adm-wave-chunk` option is the same as `--wave-chunks`, except that it is for one chunk only (but can be used multiple times) and signals that the chunk contains ADM audio metadata.
-    - Profile and level labels can be provided with the option
-    - A ADMAudioMetadataSubDescriptor descriptor is created and it sits alongside the RIFFChunkDefinitionSubDescriptor.
-- ADM Soundfield Group labels are required to reference a chunk containing ADM audio metadata. The audio labels text file provides a `chunk_id` property for identifing the chunk containing ADM audio metadata.
-    - The chunk needs to identified as containing ADM audio metadata using a ADMAudioMetadataSubDescriptor descriptor.
-    - The chunk ID is converted to the MXF generic stream ID as part of the file creation process.
+    - Sound Tracks containing channels originating from the input file will reference all the chunks from that input file using RIFFChunkReferencesSubDescriptors
+- The `--adm-wave-chunk` option is the same as `--wave-chunks` except that:
+    - It identifies only one chunk at a time (but can be used multiple times) and signals that the chunk contains ADM metadata
+    - ADM Profile/Level labels can be provided with the option
+    - An ADMAudioMetadataSubDescriptor descriptor is created and it sits alongside the RIFFChunkDefinitionSubDescriptor for the chunk
 
 ## Creating a Wave+ADM sample file
 
@@ -46,16 +88,13 @@ A Wave+ADM sample file can be created using the following example commandline gi
 
 The \<axml\> file `axml.xml` contains the data that will be written into the \<axml\> chunk. The \<chna\> text file `chna.txt` lists the audio identifiers that make up the \<chna\> chunk. The format of the text file is described in [\<chna\> Text file Definition Format](#chna-text-file-definition-format).
 
-If the source Wave file contained an \<axml\> chunk then the `--wave-chunk-data` option will override it. If the source Wave file contained a \<chna\> chunk then the `--chna-audio-ids chna.txt` option will override it.
-
 A Wave+ADM sample file can be created without a \<axml\> chunk, i.e. just a \<chna\> chunk, using the following example commandline given a Wave file (which doesn't have a \<axml\> chunk!) and a \<chna\> text file:
 
 `raw2bmx -t wave -o output.wav --chna-audio-ids chna.txt --wave input.wav`
 
-Raw PCM files can also be used as input. E.g.
-replace
+Raw PCM files can also be used as input. For example, replace:
 
-`--wave input.wave`
+`--wave input.wav`
 
 with
 
@@ -65,13 +104,13 @@ with
 
 A Wave+ADM can be converted to MXF+ADM using the following example commandline:
 
-`raw2bmx -t op1a -o output.mxf --adm-wave-chunk axml,adm_itu2076 --wave input.wave`
+`raw2bmx -t op1a -o output.mxf --adm-wave-chunk axml,adm_itu2076 --wave input.wav`
 
-The \<axml\> chunk in this example is known to contain ADM metadata and therefore the `--adm-wave-chunk` option is used. If it doesn't contain ADM metadata and should still be transferred to MXF then use the `--wave-chunks` option. The \<chna\> chunk (mapped to a MXF descriptor) is also written to the output file.
+The \<axml\> chunk in this example is known to contain ADM metadata and therefore the `--adm-wave-chunk` option is used. If it doesn't contain ADM metadata and should still be transferred to MXF then use the `--wave-chunks` option. The \<chna\> chunk (mapped to a MXF SubDescriptor) is also written to the output file.
 
-The default layout is to have mono-audio MXF tracks. This can be changed using the `--track-map` option. For example, this command will group stereo pairs into MXF tracks:
+The default layout is to have mono-audio MXF tracks. This can be changed using the `--track-map` option. For example, this command will group two stereo pairs into MXF tracks:
 
-`raw2bmx -t op1a -o output.mxf --track-map '0,1;2,3' --wave input.wave`
+`raw2bmx -t op1a -o output.mxf --track-map '0,1;2,3' --adm-wave-chunk axml,adm_itu2076 --wave input.wav`
 
 Note that the channel index is zero-based in the `--track-map` option.
 
@@ -89,62 +128,81 @@ The `--track-map` option can be used to change the audio channels. For example,
 
 A Wave+ADM can be converted to another Wave+ADM using the following example commandline:
 
-`raw2bmx -t wave -o output.wave --wave-chunks axml --wave input.wave`
+`raw2bmx -t wave -o output.wav --wave-chunks axml --wave input.wav`
 
 The `--wave-chunks` option ensures that the \<axml\> chunk is copied over (in addition to the \<chna\> chunk). The `--adm-wave-chunk` isn't required here because the Wave file format doesn't need to know which chunks contain ADM audio metadata.
 
+The `--wave-chunk-data` option could be used instead of `--wave-chunks` to override the \<axml\> chunk with the contents of an XML file. The `--chna-audio-ids` option could be used to override the \<chna\> chunk.
+
 The `--track-map` option can be used to change what is output. For example, reorder the stereo pairs:
 
-`raw2bmx -t wave -o output.wave --track-map '2,3,0,1' --wave-chunks axml --wave input.wave`
+`raw2bmx -t wave -o output.wav --track-map '2,3,0,1' --wave-chunks axml --wave input.wav`
 
-## Add ADM MCA labels to MXF+ADM
+## Extracting ADM metadata and \<chna\> information from an MXF file
 
-A ADM Soundfield Group Label Subdescriptor is created from a [MCA labels text file](./mca_labels_format.md) if the list of properties associated with the Soundfield Group contains an ADM property (the ADM properties have the prefix "ADM") or it is a ADM Soundfield Group label and there are no Audio Channels that reference it.
+The ADM metadata and \<chna\> information in an MXF file can be extracted to external files using the following example commandline:
 
-A ADM Soundfield Group label can be added using the `ADM` symbol in a [MCA labels text file](./mca_labels_format.md).
+`mxf2raw --chna-text-out chna --wave-chunks-out chunk input.mxf`
 
-`mca.txt`:
+## Add ADM MCA labels to MXF+ADM
+
+### MCA labels text file
+
+An [MCA labels text file](./mca_labels_format.md) is used to specify the Multichannel Audio Labeling (MCA) to add to an MXF file. This is an example:
 
 ```text
 0
-chL, chan=0
-chR, chan=1
-sgST, lang=eng, mca_title="Example Programme"
-ADM, chunk_id=axml, adm_audio_object_id="AO_1001"
-
-1
-chL, chan=0
-chR, chan=1
-sgST, lang=eng, mca_title="Example Programme"
-ADM, chunk_id=axml, adm_audio_object_id="AO_1002"
+ADM, chunk_id=axml, RFC5646SpokenLanguage="en-GB", MCATitle="Default", MCATitleVersion="n/a", MCAContent="PRM", MCAUseClass="FCMP", ADMAudioProgrammeID="APR_1001"
+ADM, chunk_id=axml, MCATitle="No Commentary", MCATitleVersion="n/a", MCAContent="PRM", MCAUseClass="FCMP", ADMAudioProgrammeID="APR_1002"
 ```
 
-Note the (required) `chunk_id` property for the ADM Soundfield Group Label which identifies the \<axml\> chunk containing the ADM audio metadata. The `--adm-wave-chunk` option must be used to signal that it contains ADM audio metadata.
+Each soundfield group (SG) "label line" in the text file results in the creation of a SoundfieldGroupLabelSubDescriptor unless a `chunk_id` property is present on that line (in which case a ADMSoundfieldGroupLabelSubDescriptor is created). In this example two ADMSoundfieldGroupLabelSubDescriptor instances are created.
+
+The `chunk_id` property gives the ID of the chunk carrying the associated ADM metadata. This chunk must be mapped using the `--adm-wave-chunk` commandline option (so that it's properly signalled as containing ADM metadata). In this example, both soundfield groups reference the \<axml\> chunk.
+
+The ADM Soundfield Group Label (with MCA Tag Symbol "ADM") can be specified using the symbol "ADM" at the start of the "label line". This is used by both soundfield groups in this example.
+
+Note that `bmx` permits both the SoundfieldGroupLabelSubDescriptor and the ADMSoundfieldGroupLabelSubDescriptor to use any soundfield group label.
+
+The following extra properties can be used on any line where the `chunk_id` property is present:
+* ADMAudioProgrammeID
+* ADMAudioContentID
+* ADMAudioObjectID
+
+### MXF creation commandline for MCA
+
+Example:
+
+`raw2bmx -t op1a -o output.mxf --track-map '0,1' --track-mca-labels x mca.txt --audio-layout adm --adm-wave-chunk axml --wave input.wav`
+
+In this example the MCA labels text file is called `mca.txt`.
+
+(_note_: the `x` in `--track-mca-labels` is a legacy option component and will be ignored)
 
-The MCA labels defined in `mca.txt` can be added and the ADM-described content label can be set in the audio descriptor Channel Assignment property using the following example commandline: (_note_: the `x` in `--track-mca-labels` is a legacy option component and will be ignored)
+`--audio-layout adm` populates the Channel Assignment audio descriptor property with the AudioLabelingFrameworkADMContent label.
 
-`raw2bmx -t op1a -o output.mxf --track-map '0,1' --track-mca-labels x mca.txt --audio-layout adm --adm-wave-chunk axml --wave input.wave`
+### MXF Inspection with `mxf2raw`
 
-The Soundfield Groups that use the ADM Soundfield Group Label Subdescriptor are shown using a `(ADM)` suffix in the summary output of `mxf2raw`. E.g. `ADM(ADM)` in the example `mca.txt` above. If the `--mca-detail` option is used and the Soundfield Group uses the ADM Soundfield Group Label Subdescriptor then the name used in the `SoundfieldGroups` array is `ADMSoundfieldGroup`.
+The soundfield groups that use the ADMSoundfieldGroupLabelSubDescriptor are shown using a `(ADM)` suffix in the summary output of `mxf2raw`. For example, both soundfield groups in the example above will appear as `ADM(ADM)`. If the `--mca-detail` option is used and the soundfield group uses the ADMSoundfieldGroupLabelSubDescriptor then the name used in the `SoundfieldGroups` array is `ADMSoundfieldGroup`.
 
-## \<chna\> Text File Definition Format
+## \<chna\> Text File Format
 
-The \<chna\> text file contains the list of ADM audio identifiers that make up the \<chna\> chunk. The number of tracks and UIDs is automatically calculated.
+`bmx` uses a \<chna\> text file for input/output of \<chna\> information. This is the information stored in the \<chna\> chunk in Wave files and in the ADM_CHNASubDescriptor in MXF files.
 
-The \<chna\> text file consists of a set of name/value property pairs separated by a newline. The name/value pair uses the first ':' character as a separator. A '#' character signals the start of a comment.
+The \<chna\> text file contains a list of ADM audio identifiers. There is a set of name/value property pairs for each audio identifier, separated by a newline. The name/value pair uses the first ':' character as a separator. A '#' character signals the start of a comment.
 
-The properties for each audio identifier are as follows.
+The properties for each audio identifier are as follows:
 
-- `track_index`: The index of the track in the Wave file, *starting from 1*. A value 0 represents a null / placeholder entry.
-- `uid`: The audioTrackUID value of the track.
-- `track_ref`: The audioTrackFormatID reference for the track.
-- `pack_ref`: The audioPackFormatID reference for the track.
+- `track_index`: The index of the track in the Wave file or the index of the channel in the MXF Sound Track. The index *starts from 1* in both cases. A value 0 represents a null / placeholder entry.
+- `uid`: The audioTrackUID value
+- `track_ref`: The linked audioTrackFormatID or audioChannelFormatID value
+- `pack_ref`: The linked audioPackFormatID value
 
 Each audio identifier is started by a `track_index` property.
 
-A `track_index` 0 represents a null / placeholder entry that is used to support Wave file updates. These entries are stripped when mapping to MXF.
+Note that the additional \<chna\> properties are not stored in the \<chna\> text file (numTracks and numUIDs in Wave files; NumLocalChannels and NumADMAudioTrackUIDs in MXF files). These are discarded upon read of Wave/MXF files, and automatically calculated upon write of Wave/MXF files.
 
-An example \<chna\> text file is shown below. It describes 2 stereo pairs, each with "front left" and "front right" channels.
+An example \<chna\> text file is shown below. It describes two stereo pairs, each with "front left" and "front right" channels.
 
 ```text
 track_index: 1
diff --git a/docs/mca_labels_format.md b/docs/mca_labels_format.md
index dc282a3b..3b61f98f 100644
--- a/docs/mca_labels_format.md
+++ b/docs/mca_labels_format.md
@@ -1,20 +1,20 @@
 # MCA Labels Format
 
-The `--track-mca-labels` option in raw2bmx and bmxtranswrap can be used to add Multi-channel Audio Labels as specified in SMPTE ST 377-4:2021. The format for the text file that is passed to that option is described in this document.
+The `--track-mca-labels` option in raw2bmx and bmxtranswrap can be used to add Multichannel Audio Labeling as specified in SMPTE ST 377-4:2021. The format for the text file that is passed to that option is described in this document.
 
 ## General Layout
 
-The text file contains one of the following line types:
+Each line in the text file is one of the following line types:
 
 - audio track index
-- audio channel (CH), soundfield group (SG) or group of soundfield group (GOSG) label
+- Label line specifying the audio channel (CH), soundfield group (SG) or group of soundfield group (GOSG)
 - empty
 
 A `#` character can be used to add a comment.
 
-The file defines the set of audio labels to include for each MXF audio track. The audio tracks are identified by an integer index starting from 0 and incrementing by 1 in the order that the audio tracks are written (the Track ID order).
+The file defines the set of audio labels to include for each MXF audio track (aka Sound Track). The audio tracks are identified by an integer index starting from 0 and incrementing by 1 in the order that the audio tracks are written (the Track ID order).
 
-A set of labels for an audio track starts with a line containing the index and is followed by lines defining audio labels. There can be multiple channel CH label lines, 0 or 1 SG label lines and 0 or more GOSG label lines.
+A set of labels for an audio track starts with a line containing the index and is followed by label lines (each one defining an audio label). These audio labels can include zero or more of each type (CH, SG, GOSG).
 
 An empty line is used to signal the start of a new audio track.
 
@@ -22,7 +22,7 @@ An empty line is used to signal the start of a new audio track.
 
  A label line consists of the value of the MCA Tag Symbol label property, followed by a comma and a comma-separated list of name`=`value pairs of properties for that label.
 
- The label identifies either a CH (e.g. `chL` for Left), SG (e.g. `sg51` for 5.1) or GOSG (e.g. `ggMPg` for Main Program). The list of supported labels can be found in the [AppMCALabelHelper.cpp](../src/apps/AppMCALabelHelper.cpp) source code file. The supported names are listed below.
+ The label identifies either a CH (e.g. `chL` for Left), SG (e.g. `sg51` for 5.1) or GOSG (e.g. `ggMPg` for Main Program). The list of supported labels can be found in the [AppMCALabelHelper.cpp](../src/apps/AppMCALabelHelper.cpp) source code file.
 
  The label properties are described in the next section, including how to insert characters such as commas into values.
 
@@ -40,8 +40,6 @@ The `repeat` property is used to decide whether to repeat a SG or GOSG label tha
 
 The first instance of a SG or GOSG label with a given `id` will always be stored in the MXF track's file descriptor. Subsequent SG or GOSG labels with the same `id` will be stored as a copy of the earlier label if `repeat` is True.
 
-The `chunk_id` property is required for the `ADM` SG label. It is used to set the `RIFFChunkStreamID_link2` property value in the `ADM` SG label to the ID of the MXF generic stream that contains the ADM audio metadata chunk (with the given `chunk_id` chunk ID).
-
 The following string value properties can be used:
 
 - RFC5646SpokenLanguage (alternative is "lang")
@@ -60,22 +58,23 @@ The following string value properties can be used:
 - MCASpokenLanguageAttribute
 - RFC5646AdditionalSpokenLanguages
 - MCAAdditionalLanguageAttributes
-- ADMAudioProgrammeID_ST2131
-- ADMAudioContentID_ST2131
-- ADMAudioObjectID_ST2131
+- ADMAudioProgrammeID
+- ADMAudioContentID
+- ADMAudioObjectID
 
 The "lang" name can be used instead of "RFC5646SpokenLanguage".
 
 The name may omit the "MCA" prefix, e.g. "TitleVersion" is accepted. The name matching is case-insenstive, e.g. "titleversion" is accepted. Underscores are ignored, e.g. "title_version" is accepted.
 
-The ADM properties, which are the properties with the "ADM" prefix, may also omit the "_ST2131" suffix. The ADM properties can only be used in a `ADM` SG label.
-
 The property value may be between quotation marks, either single or double quotes.
 
 Some special characters (e.g. used in RFC5646AdditionalSpokenLanguages and MCAAdditionalLanguageAttributes) can be set by using the `\` escape character. They are tab `\t` (0x09), line feed `\n` (0x0a) and carriage return `\r` (0x0d).
 
 The `\` escape character can be used before special characters, e.g. characters such as `,` and `#` when not using quotation marks or `"` when using double quotes. A `\` character can be inserted using a double backslash `\\`.
 
+See [audio_definition_model.md](./audio_definition_model.md) for an explanation, and examples, of using the ADM properties (those with the "ADM" prefix) and the `chunk_id` property.
+
+
 ## Example Files
 
 This example below is an English language Main Program 5.1.
@@ -112,4 +111,3 @@ sgST, id=sg1, repeat=false
 ggAPg, id=gosg1, repeat=false
 ```
 
-See [audio_definition_model.md](./audio_definition_model.md#add-adm-mca-labels-to-mxfadm) for an example that uses the ADM properties.