TrueHD Atmos to DD+ Atmos Encoding Guide

Comprehensive Tutorial for Converting TrueHD Atmos to DD+ Atmos

Introduction Step 1: Decode TrueHD Atmos Step 2: Interleave WAVs Step 3: Encode to DD+ Atmos Considerations Atmos Decode Script Conclusion

Introduction

This guide provides a step-by-step tutorial on converting a TrueHD Atmos audio track to a Dolby Digital Plus (DD+) Atmos format. This process involves decoding the TrueHD track into individual WAV files, interleaving them into a single multichannel WAV file, and then encoding that file into DD+ Atmos using the Dolby Encoding Engine (DEE).

Dolby Atmos is a cutting-edge audio technology that creates an immersive 3D sound experience. TrueHD Atmos is commonly found on Blu-ray discs, while DD+ Atmos is often used for streaming. This guide is designed for professionals and enthusiasts who want to retain the integrity of the Atmos metadata while converting between these formats.

Step 1: Decode TrueHD Atmos to 16 Mono WAVs

Tools Required

• Plazik's atmos_decode.py script
• Dolby Reference Player

The first step involves decoding the TrueHD Atmos track into its individual components (channels). TrueHD Atmos can include multiple objects and channels, typically in a 9.1.6 setup (nine speakers, one subwoofer, and six height channels).

Process

1. Run Plazik's atmos_decode.py: This Python script works in conjunction with the Dolby Reference Player to extract the individual channels from the TrueHD stream.

   python atmos_decode.py --input source.truehd --output-dir output_wavs

2. Check the Output: After running the script, verify that you have 16 mono WAV files in the output directory. Each file represents a different channel in the Atmos configuration (e.g., Front Left, Front Right, Center, etc.).

Step 2: Interleave the Mono WAVs into a Single 16-Channel WAV

Tools Required

• FFmpeg

Once you have the 16 individual WAV files, the next step is to combine them into a single interleaved 16-channel WAV file.

Process

1. Use FFmpeg to Interleave WAVs: FFmpeg is a powerful tool for handling multimedia files and streams. Use the following command to interleave the mono WAV files into a single multichannel WAV file:

   ffmpeg -i "input_channel1.wav" -i "input_channel2.wav" -i "input_channel3.wav" -i "input_channel4.wav" \
   -i "input_channel5.wav" -i "input_channel6.wav" -i "input_channel7.wav" -i "input_channel8.wav" \
   -i "input_channel9.wav" -i "input_channel10.wav" -i "input_channel11.wav" -i "input_channel12.wav" \
   -i "input_channel13.wav" -i "input_channel14.wav" -i "input_channel15.wav" -i "input_channel16.wav" \
   -filter_complex "[0:a][1:a][2:a][3:a][4:a][5:a][6:a][7:a][8:a][9:a][10:a][11:a][12:a][13:a][14:a][15:a]join=inputs=16:channel_layout=9.1.6" \
   -acodec pcm_s16le output_interleaved.wav

Step 3: Encode the Combined WAV to DD+ Atmos

Tools Required

• Dolby Encoding Engine (DEE)
• Encoding Template (e.g., wav_encode_to_atmos_ddp_ec3.xml)

With the single interleaved WAV file ready, the next step is to encode it into a DD+ Atmos stream.

Process

1. Prepare the Encoding Template: The wav_encode_to_atmos_ddp_ec3.xml template will guide the Dolby Encoding Engine on how to process the input WAV file. Ensure the template is configured correctly for your specific needs.
2. Run the Encoding Process: Use the Dolby Encoding Engine to encode the 16-channel WAV file into DD+ Atmos.

   dee --input_file output_interleaved.wav --template wav_encode_to_atmos_ddp_ec3.xml --output_file output_atmos_ddp.ec3

3. Verify the Output: Ensure that the output file (output_atmos_ddp.ec3) meets your requirements, including the correct channel layout, bitrate, and Atmos metadata.

Considerations and Tips

Bitrate Selection

DD+ Atmos typically supports bitrates up to 1024 kbps. Adjust the bitrate in the encoding template according to your needs (e.g., streaming constraints).

Channel Mapping

Ensure the channels in your interleaved WAV are correctly mapped to the expected layout in the Dolby Encoding Engine. Incorrect mapping could result in improper playback on Atmos-enabled devices.

Testing and Validation

After encoding, test the output file on various devices to ensure that the Atmos metadata and audio are correctly interpreted by different playback systems.

Documentation and Support

Consult the official Dolby documentation for the latest best practices and technical details. Dolby provides extensive resources to help you understand and use their tools effectively.

Atmos Decode Script

Below is the `atmos_decode.py` script used for decoding TrueHD Atmos streams:

# atmos_decode.py
import os
import argparse
from subprocess import call

def decode_atmos(input_file, output_dir):
    if not os.path.exists(output_dir):
        os.makedirs(output_dir)
    command = f'dolby_ref_player --input {input_file} --output {output_dir} --decode --mode atmos'
    call(command, shell=True)

def main():
    parser = argparse.ArgumentParser(description='Decode TrueHD Atmos to mono WAVs.')
    parser.add_argument('--input', required=True, help='Path to the input TrueHD file.')
    parser.add_argument('--output-dir', required=True, help='Directory to save the output WAV files.')
    
    args = parser.parse_args()
    decode_atmos(args.input, args.output_dir)

if __name__ == "__main__":
    main()
        

This script decodes a TrueHD Atmos track into its individual channel WAV files using the Dolby Reference Player. Adjust the paths and filenames as necessary to match your environment.

Conclusion

By following these steps, you can successfully convert a TrueHD Atmos track to a DD+ Atmos file suitable for distribution or streaming. This method leverages advanced tools like Plazik's `atmos_decode.py`, FFmpeg, and the Dolby Encoding Engine to maintain the integrity of the original Atmos experience while adapting it for different formats and bitrates.

Thorough testing and validation are crucial to ensure that the final product meets the high standards expected of Dolby Atmos content. For more information and updates, visit the Deew GitHub page.

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