Audio Channel Extractor & Concatenator

A powerful Bash script designed to easily extract and concatenate separate audio WAV channels from multitrack container files (32 channels). Perfect for audio engineers and post-production workflows dealing with multi-channel audio recordings split across multiple files.

Features

• 🎚️ Multi-channel Extraction: Extract individual channels from 32-channel WAV files
• 🔄 File Concatenation: Automatically join multiple audio chunks into continuous channels
• 🖱️ Drag & Drop Interface: Simple folder selection with drag & drop support
• ⚙️ Customizable Settings: Adjust channel count and output naming
• 📊 Real-time Progress: Detailed processing summary and status updates
• 🐛 Debug Logging: Comprehensive log file for troubleshooting

Prerequisites

• FFmpeg must be installed and accessible in your system PATH
• Bash shell environment (Linux, macOS, or Windows with WSL/Cygwin)
• Audio files in WAV format with multiple channels

Installation

1. Download the script file 'chunk_extract.sh']
2. Make it executable:

   chmod +x chunk_extract.sh

3. Ensure FFmpeg is installed:

   # Ubuntu/Debian
   sudo apt install ffmpeg
   
   # macOS with Homebrew
   brew install ffmpeg
   
   # Windows (via chocolatey)
   choco install ffmpeg

Usage

Basic Usage

./chunk_extract.sh

Step-by-Step Process

1. Run the script - Execute the script in your terminal
2. Folder Selection - Either:
   • Drag and drop your audio folder into the terminal
   • Press Enter to use the current directory
3. Configuration - Set:
   • Number of channels (default: 32)
   • Output file prefix (default: "CH")
4. Processing - Script automatically:
   • Detects all WAV files in the folder
   • Sorts them numerically
   • Extracts and concatenates each channel
   • Creates individual output files for each channel

Input File Requirements

• Files must have .WAV extension (uppercase)
• Files should be named in a way that sorts correctly (e.g., 00000001.WAV, 00000002.WAV)
• Each file should contain the same number of channels
• Files should be sequential parts of the same recording

Output Files

The script creates individual WAV files for each channel:

• CH1.wav - Channel 1 (complete concatenated audio)
• CH2.wav - Channel 2
• CH3.wav - Channel 3
• ... up to the specified channel count

Configuration Options

Modifiable Variables in Script

CHUNK_PATTERN="*.WAV"      # File pattern to match
CHANNEL_COUNT=32          # Default number of channels
OUTPUT_PREFIX="CH"        # Output file prefix

Runtime Options

• Channel Count: Specify during execution (supports any number)
• Output Prefix: Custom naming for output files
• Input Folder: Any directory containing your audio chunks

Technical Details

How It Works

1. File Discovery: Scans directory for WAV files and sorts them
2. Filter Graph Construction: Builds dynamic FFmpeg filter graphs for each channel
3. Channel Extraction: Uses FFmpeg's channelmap to isolate individual channels
4. Concatenation: Joins channel segments across all input files
5. Output Generation: Creates PCM S16LE WAV files for each channel

FFmpeg Commands

The script generates FFmpeg commands like:

ffmpeg -i 00000001.WAV -i chunk2.WAV -filter_complex \
"[0]channelmap=0-0:mono[0_0];[1]channelmap=0-0:mono[0_1];\
[0_0][0_1]concat=n=2:v=0:a=1[out0]" -map "[out0]" -c:a pcm_s16le CH1.wav

Error Handling

• Folder Validation: Checks if specified directory exists
• File Detection: Verifies audio files are present
• Input Validation: Validates numeric inputs for channel count
• Process Monitoring: Checks FFmpeg exit status for success/failure

Troubleshooting

Common Issues

1. "No audio files found"

   • Ensure files have .WAV extension (uppercase)
   • Check file permissions in the directory

2. FFmpeg not found

   • Install FFmpeg and ensure it's in your PATH
   • Verify with ffmpeg -version

3. Permission denied

   • Make script executable: chmod +x script_name.sh

4. Processing errors

   • Check log.txt for detailed FFmpeg commands and errors
   • Verify all input files have the same channel layout

Log File

The script creates log.txt with:

• FFmpeg commands executed
• Debug information
• Error details (if any)

Examples

Basic Example

./chunk_extract.sh
# Uses current directory, 32 channels, "CH" prefix

Custom Configuration

./chunk_extract.sh
# When prompted:
# - Folder: /path/to/audio/chunks
# - Channels: 16
# - Prefix: "DRUM_"
# Output: DRUM_1.wav through DRUM_16.wav

License

GNU GPLv3 Created by MatiqBushwick.

Contributing

Feel free to:

• Report issues
• Suggest improvements
• Submit pull requests

Support

For issues and questions:

1. Check the troubleshooting section
2. Examine the log.txt file
3. Ensure FFmpeg is properly installed
4. Verify input file format and structure

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Note: This script is designed for professional audio workflows and handles large multitrack sessions efficiently. Always backup your original files before processing.