Add ALAC to FLAC Conversion Support

[Ardakilic]

Overview

This PR extends the FLAC-only audio converter to support ALAC (Apple Lossless Audio Codec) files, enabling conversion from ALAC to FLAC with intelligent quality-based processing rules.

🎯 Key Features Added

ALAC Detection and Processing

• Smart Format Detection: Automatically detects ALAC files (.m4a extension) in source directories
• Dual Format Support: Maintains existing FLAC functionality while adding comprehensive ALAC support
• Intelligent Dependency Management: Automatically determines when FFmpeg is required based on file types present

Quality-Based Conversion Logic

• 16-bit Standard Quality: Direct conversion without quality reduction for 16-bit/44.1kHz and 16-bit/48kHz ALAC files
• Hi-Resolution Processing: Converts hi-res ALAC files (24-bit, >48kHz, or >16-bit) to 16-bit/44.1kHz FLAC
• Preservation of Audio Quality: Smart conversion rules ensure optimal output quality for each input type

Enhanced Audio Processing Pipeline

• FFmpeg Integration: Seamless integration with FFmpeg for ALAC processing alongside existing SoX support
• Metadata Preservation: Maintains audio metadata during ALAC to FLAC conversion when possible
• Docker Compatibility: Full Docker support for both FLAC and ALAC processing workflows

🔧 Technical Implementation

Core Changes in main.go

• Extended AudioInfo struct with Format field for multi-format support
• Added getALACInfo() function for ALAC file analysis
• Implemented processALAC() function with conversion logic
• Created hasALACFiles() for directory scanning and dependency detection
• Enhanced processAudioFile() to handle both FLAC and ALAC formats
• Updated conversion logic to support format-specific processing rules

Dependency Management

• Smart FFmpeg Detection: Only requires FFmpeg when ALAC files are present
• Backward Compatibility: Projects with only FLAC files continue to work with SoX alone
• Error Handling: Graceful fallback and clear error messages for missing dependencies

Updated Documentation

• README.md: Added ALAC features, FFmpeg requirements, and updated installation instructions
• Development.md: Enhanced with ALAC implementation details and testing guidelines
• Feature Lists: Updated all feature descriptions to reflect dual-format support

🧪 Comprehensive Testing

Test Suite Expansion

• 30+ New Test Functions: Added comprehensive ALAC-specific test coverage
• HTTP Mocking: Implemented robust HTTP client mocking for update functionality
• Edge Case Coverage: Extensive testing of error conditions, format detection, and conversion scenarios
• Integration Testing: Full workflow testing for both ALAC and FLAC processing

Coverage Improvements

• Initial Coverage: Started at ~66% test coverage
• Final Coverage: Achieved 73.0% test coverage
• Test Optimization: Removed ~700 lines of duplicate test code while maintaining coverage
• Quality Assurance: All tests pass consistently across different scenarios

Test Categories Added

• ALAC file detection and processing
• Format-specific conversion logic testing
• FFmpeg dependency management
• Error handling and recovery scenarios
• Docker integration with ALAC support
• Metadata preservation workflows

📋 Files Modified

Core Application

• main.go - Extended with full ALAC support and smart conversion logic
• main_test.go - Comprehensive test suite expansion and optimization

Documentation

• README.md - Updated features, requirements, and installation instructions
• Development.md - Enhanced development guidelines and technical details

Configuration

• Docker integration maintained and extended for ALAC support
• GitHub Actions compatibility preserved

🔄 Backward Compatibility

• 100% Backward Compatible: All existing FLAC functionality preserved
• No Breaking Changes: Existing workflows continue to work unchanged
• Progressive Enhancement: ALAC support is additive, not disruptive
• Dependency Optimization: FFmpeg only required when ALAC files are present

🚀 Usage Examples

Converting ALAC Files

# Convert ALAC files from source to target directory
./lilt -source /path/to/alac/files -target /path/to/output

# Include image files during ALAC conversion
./lilt -source /path/to/alac/files -target /path/to/output -copy-images

# Use Docker for ALAC processing
./lilt -source /path/to/alac/files -target /path/to/output -use-docker

Mixed Format Processing

# Process directories containing both FLAC and ALAC files
./lilt -source /path/to/mixed/audio -target /path/to/output

📊 Performance Impact

• Minimal Overhead: ALAC detection adds negligible processing time
• Efficient Processing: Smart dependency detection avoids unnecessary tool invocation
• Memory Efficient: Maintains low memory footprint for both formats
• Scalable: Handles large directories with mixed audio formats effectively

🔍 Quality Assurance

• All existing functionality thoroughly tested and verified
• New ALAC features extensively tested with edge cases
• Docker integration validated for both formats
• Cross-platform compatibility maintained
• Error handling improved with clear user feedback

🎉 Benefits

• Expanded Format Support: Now handles both major lossless audio formats
• Intelligent Processing: Smart conversion rules optimize output quality
• Maintained Simplicity: Complex logic hidden behind simple interface
• Production Ready: Comprehensive testing ensures reliability
• Future-Proof: Architecture supports additional formats if needed

This PR transforms the project from a FLAC-only converter to a comprehensive lossless audio conversion tool while maintaining all existing functionality and performance characteristics.

[Copilot]

Pull Request Overview

This PR transforms the FLAC-only audio converter into a comprehensive lossless audio conversion tool by adding support for ALAC (Apple Lossless Audio Codec) files while maintaining full backward compatibility.

• Adds complete ALAC to FLAC conversion with intelligent quality-based processing
• Extends existing FLAC functionality to handle both formats seamlessly
• Implements smart dependency management requiring FFmpeg only when ALAC files are present

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
main.go	Core implementation of ALAC support including format detection, conversion logic, and enhanced audio processing pipeline
main_test.go	Comprehensive test suite expansion with 30+ new ALAC-specific tests and coverage improvements
README.md	Updated documentation to reflect dual-format support, FFmpeg requirements, and new usage examples
Development.md	Enhanced development guidelines with ALAC implementation details and testing instructions

Comments suppressed due to low confidence (1)

main_test.go:1

• The comment indicates this test should avoid triggering HTTP requests, but the test doesn't actually verify that no HTTP calls are made. Consider using a mock HTTP client or verifying that the error occurs before any network operations.

package main

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