Introduction of the MPEG-H 3D Audio Low Complexity Profile Decoder

The advent of object-based audio and scene-based audio has revolutionized the 3D sound experience. Traditional channel-based coding expects the capture and playback geometric locations to be exactly the same for best reconstruction of the audio scene. On the other hand, object-based audio coding represents discrete sound sources in the audio scene. The positional information of each of the objects in the audio scene is conveyed in the form of metadata. Scene-based audio coding attempts to reconstruct the sound field at the playback end using the coded higher order ambisonics (HOA) information. In case of both object-based and scene-based audio, the rendering algorithm can adapt based on the configuration of the playback end loudspeaker arrangement, thus making the sound experience agnostic to the configuration of speakers at the playback end.

MPEG-H 3D Audio is a coding standard that supports traditional channel-based, object-based and scene-based audio coding. The immersive 3D sound experience created by MPEG-H 3D Audio is significantly enhanced in comparison with the traditional channel-based multichannel programs and playback systems.

The MPEG-H 3D Audio Low Complexity Profile decoder supports all specified formats, including channel-based audio, object-based audio and scene-based audio via higher order ambisonics (HOA). State-of-the-art MPEG-H 3D Audio Low Complexity Profile decoders according to ISO/IEC 23008-3:2019/AMD 2:2020 also support the MPEG-H 3D Audio Baseline Profile, which is a subset of the MPEG-H 3D Audio Low Complexity Profile. The MPEG-H 3D Audio Baseline Profile does not support scene-based audio/HOA.

Introduction to MPEG-H 3D Audio Low Complexity Profile Decoder APIs

Files to be included are

• impeghd_api.h
• impeghd_type_def.h
• impeghd_memory_standards.h
• impeghd_error_codes.h
• impeghd_config_params.h

Decoder APIs

API Call	Description
ia_mpegh_dec_get_lib_id_strings	Gets the decoder library name and version number details
ia_mpegh_dec_create	Gets the memory requirements size and allocate required memory
ia_mpegh_dec_init	Decodes the header/initialization bytes
ia_mpegh_dec_execute	Decodes the input frame data
ia_mpegh_dec_delete	Frees the allocated memories for the decoder

Flowchart of calling sequence

Building the MPEG-H 3D Audio Low Complexity Profile Decoder

Building for Unix/MacOS

• Makefiles for building the MPEG-H 3D Audio Low Complexity Profile decoder library and application are provided in build/makefile folder.
• These makefiles are common for Unix/MacOS builds.
• If compiling for non-native platforms, ensure that the compiler and sysroot are updated.
• Supported arch values are x86, x86_64, armv7 and armv8.
• Build the library with support upto low complexity profile level 3 using the below command:

$ make -f Makefile_lib clean all ARCH=<arch>

• Build the library with support upto low complexity profile level 4 using the below command:

$ make -f Makefile_lib clean all ARCH=<arch> LC_LEVEL_4=1

• Build the application using the below command:

$ make -f Makefile clean all	ARCH=<arch>

Building for Windows

• MSVS projects files required for building the MPEG-H 3D Audio Low Complexity Profile decoder library and application are provided in build/msvs folder.
• These MSVS project files correspond to "MSVS 2017". If the MSVS version is different, then the SDK and toolset will have to be updated accordingly.

Using CMake

Users can also use cmake to build for x86, x86_64, armv7, armv8 and Windows (MSVS project) platforms.

Building for native platforms

Run the following commands to build the MPEG-H 3D Audio Low Complexity Profile Decoder for native platform:

Go to the root directory(libmpegh/) of the MPEG-H 3D Audio Low Complexity Profile Decoder. Create a new folder in the project root directory and move to the newly created folder.

$ cd <path to libmpegh>
$ mkdir bin
$ cd bin

Run the below command to configure the project for default build. The default build has support upto low complextiy profile level 3.

$ cmake ..

The build option LC_LEVEL_4 can be used to configure the project to support low complexity profile level 4. Run the below command to configure the project to create a build that supports low complexity profile level 4.

$ cmake .. -DLC_LEVEL_4=ON

To build the project run the below command.

$ cmake --build .

Cross-compiling

Run the following commands to cross compile for x86, ARMv7 or ARMv8: Go to the root directory(libmpegh/) of the MPEG-H 3D Audio Low Complexity Profile Decoder. Create a new folder in the project root directory and move to the newly created folder.

$ cd <path to libmpegh>
$ mkdir bin
$ cd bin

Run the below command to configure the project for default build. The default build has support upto low complextiy profile level 3.

$ cmake .. -DCMAKE_TOOLCHAIN_FILE=../toolchain_<arch>.cmake

The build option LC_LEVEL_4 can be used to configure the project to support low complexity profile level 4. Run the below command to configure the project to create a build that supports low complexity profile level 4.

$ cmake .. -DCMAKE_TOOLCHAIN_FILE=../toolchain_<arch>.cmake -DLC_LEVEL_4=ON

To build the project run the below command.

$ cmake --build .

Creating MSVS project files

To create MSVS project files for the MPEG-H 3D Audio Low Complexity Profile decoder from cmake, run the following commands: Go to the root directory(libmpegh/) of the MPEG-H 3D Audio Low Complexity Profile Decoder. Create a new folder in the project root directory and move to the newly created folder.

$ cd <path to libmpegh>
$ mkdir bin
$ cd bin
$ cmake -G "Visual Studio 15 2017" ..

The above command creates MSVS 2017 project files. If the version is different, modify the generator name accordingly. The MPEG-H 3D Audio Low Complexity Profile decoder can be built using these project files.

Using Autoconf

Run the following commands to build using autoconf tools:

Go to the root directory(libmpegh/) of the MPEG-H 3D Audio Low Complexity Profile Decoder.

$ cd <path to libmpegh>
$ autoreconf -if
$ ./configure
$ make 

Running the MPEG-H 3D Audio Low Complexity Profile Decoder

The MPEG-H 3D Audio Low Complexity Profile Decoder can be run by providing command-line parameters(CLI options) directly or by providing a parameter file as a command line argument.

Command line usage :

<exceutable> -ifile:<input_file> -ofile:<out_file> [options]

[options] can be,
[-pcmsz:<pcmwordsize>]
[-target_loudness:<target_loudness>]
[-effect:<drc_effect_type>]
[-cicp:<target_layout>]
[-ilsi:<lsi_file>]
[-isdi:<sd_file>]
[-iei:<ei_file>]
[-ibrir:<brir_file>]
[-out_fs:<output_samp_freq>]
[-ext_ren:<extrn_rend_flag>]

where,
  <inputfile>        is the input MPEGH file name.
  <outputfile>       is the output file name.
  <pcmwordsize>      is the bits per sample info.
  <target_loudness>  is target loudness in dB.
  <drc_effect_type>  is drc effect type.
  <target_layout>    is target speaker layout.
        Description in format Front/Surr.LFE
        1: 1/0.0    - C
        2: 2/0.0    - L, R
        3: 3/0.0    - C, L, R
        4: 3/1.0    - C, L, R, Cs
        5: 3/2.0    - C, L, R, Ls, Rs
        6: 3/2.1    - C, L, R, Ls, Rs, LFE
        7: 5/2.1    - C, Lc, Rc, L, R, Ls, Rs, LFE
        8: NA
        9: 2/1.0    - L, R, Cs
        10: 2/2.0   - L, R, Ls, Rs
        11: 3/3.1   - C, L, R, Ls, Rs, Cs, LFE
        12: 3/4.1   - C, L, R, Ls, Rs, Lsr, Rsr, LFE
        13: 11/11.2 - C, Lc, Rc, L, R, Lss, Rss, Lsr, Rsr, Cs, LFE, LFE2, Cv, Lv, Rv, Lvss, Rvss,
                      Ts, Lvr, Rvr, Cvr, Cb, Lb, Rb
        14: 5/2.1   - C, L, R, Ls, Rs, LFE, Lv, Rv
        15: 5/5.2   - C, L, R, Lss, Rss, Ls, Rs, Lv, Rv, Cvr, LFE, LFE2
        16: 5/4.1   - C, L, R, Ls, Rs, LFE, Lv, Rv, Lvs, Rvs
        17: 6/5.1   - C, L, R, Ls, Rs, LFE, Lv, Rv, Cv, Lvs, Rvs, Ts
        18: 6/7.1   - C, L, R, Ls, Rs, Lbs, Rbs, LFE, Lv, Rv, Cv, Lvs, Rvs, Ts
        19: 5/6.1   - C, L, R, Lss, Rss, Lsr, Rsr, LFE, Lv, Rv, Lvr, Rvr
        20: 7/6.1   - C, Leos, Reos, L, R, Lss, Rss, Lsr, Rsr, LFE, Lv, Rv, Lvs, Rvs
		Note: CICP 13 is applicable for baseline profile streams with only object audio.
  <lsi_file>         bitstream file with local setup information.
  <sd_file>          bitstream file with scene displacement information.
  <ei_file>          bitstream file with element interaction information.
  <brir_file>        bitstream file with binaural renderer impulse response data.
  Note: The <lsi_file>, <sd_file>, <ei_file> and <brir_file> are bitstream files expected from the user.
        The bitstream syntax is specified in the MPEG-H specification document.
  <output_samp_freq> desired sampling frequency of the output stream -
                     invokes resampler if needed.
  <extrn_rend_flag>  flag to enable external rendering interfaces creation.
                     Enabling this flag creates external rendering interface
                     bitstreams in the same location as decoder executable

Sample CLI:

<mpegh_dec_exe> -ifile:in_file.mhas -ofile:out_file.wav -pcmsz:16 					 

Using paramfile :

The same CLI options can be provided to the MPEG-H 3D Audio Low Complexity Profile decoder via a parameter file.

Parameter file can be used to run multiple files in a single decoder instance.

Default parameter file name: paramfilesimple.txt

Apart from the facility to invoke command line options, there are certain special options available that can be set in the parameter file.

Below is the list of all such parameters:

@Input_path  <Path to Input streams location>
@Output_path <Path to write output PCM/WAVs location>
@Start
<CLI options>
@Stop

Any CLI can be invoked only after @Start.

@Stop indicates end of CLI option processing.

Any CLI mentioned after @Stop will not be processed.

In case there are multiple @Start and @Stop, only the options between the first @Start and @Stop will be processed.

A sample paramfilesimple.txt can be found in build/msvs folder.

The Parameter file can be given as an argument to the application with the path specified.

The input and the output paths in parameter file should either be relative to the executable path or the absolute paths.

If no argument is given, by default the application reads the test vectors names from the parameter file located in the same directory as executable, with the name as paramfilesimple.txt.

Sample Usage:

<mpegh_dec_exe> -paramfile:paramfilesimple.txt

For more details, refer to Section 3.1 of IA-MPEG-H-3D-Audio-Dec-GSG.doc

Smoke testing the MPEG-H 3D Audio Low Complexity Profile Decoder

A Sample test suite is provided in the workspace. The contents of the testsuite are described below.

• smoke_test_suite/inp/ - Contains .mhas and .mp4 sample streams. The decoded output of a pair of .mhas and .mp4 files will be bit-identical.

• smoke_test_suite/ref/ - Contains decoded output in wav format for reference.

• smoke_test_suite/run_smoke.py - Sample python script that runs the smoke test suite. This script uses executable with path as an argument.

  Example : python run_smoke.py ./<exe_name>

Validating the MPEG-H 3D Audio Low Complexity Profile Decoder

The MPEG-H 3D Audio Low Complexity Profile decoder has been tested with all the conformance streams as specified by ISO/IEC 23008-9

Building the Documentation of the MPEG-H 3D Audio Low Complexity Profile Decoder

Documentation can be generated with the doxygen utility for the MPEG-H 3D Audio Low Complexity Profile Decoder. Follow the below commands to generate the documentation.

$ cd docs
$ doxygen doxy.conf

Documentation will be generated in docs/documentation folder. Browse through the documentation from index.html located in docs/documentation/html folder.

Additional Documents

Brief description about documents present in docs folder

• IA-MPEG-H-3D-Audio-Dec-API.doc - Describes Application Program Interface for the MPEG-H 3D Audio Low Complexity Profile Decoder.
• IA-MPEG-H-3D-Audio-Dec-BP.doc - Describes the build procedure for the MPEG-H 3D Audio Low Complexity Profile Decoder on Unix/MacOS platforms.
• IA-MPEG-H-3D-Audio-Dec-DS.doc - Describes features supported by the MPEG-H 3D Audio Low Complexity Profile Decoder, memory requirements and computational complexity on x86, x86_64, armv7 and armv8 platforms. The details presented in the data sheet document are for low complexity profile level 3 decoder. The memory requirements and complexity are slightly higher for low complexity profile level 4 decoder.
• IA-MPEG-H-3D-Audio-Dec-GSG.doc - Getting Started Guide for the MPEG-H 3D Audio Low Complexity Profile Decoder.
• IA-MPEG-H-3D-Audio-Dec-TR.doc - Documents the conformance test report for the MPEG-H 3D Audio Low Complexity Profile decoder on x86, x86_64, armv7 and armv8 platforms.

Web Browser Plug-in Demo

A demonstartion of how the MPEG-H 3D Audio decoder may be integrated and used in browsers is added. Please refer to the document IA-MPEG-H-3D-Audio-Dec-Browser-Plugin-UG.doc for running the demo.

Guidelines working with GitHub

Please refer to the guildelines for the following processes

• Reporting issues
• Creating Pull Request
• Commit message standards

Disclaimer

• In no event shall Ittiam (or Dolby or any of their affiliates, successors, or contributors) be liable to any party for direct, indirect, special, incidental, or consequential damages, including lost profits, arising out of the use of this software and its documentation, even if ittiam has been advised of the possibility of such damage.
• Ittiam provides the information on an "As-is" basis and makes no warranties regarding any information or licenses provided on or through it and disclaims liability for damages resulting from using the license information.
• Redistributions of source code must retain the above copyright notice, the original license file and the disclaimer.
• One should have a valid third-party subscription/license, if any, required to use this software.
• Ittiam has no obligation to provide maintenance, support, updates, enhancements, or modifications.

License

A BSD 3-Clause-Clear license is applicable. Refer to the LICENSE file together with the LICENSE2 file.