feat: Add --enforce-output-format flag with FLAC, MP3, and ALAC support

[Ardakilic]

This PR introduces a new --enforce-output-format flag that allows users to standardize their entire audio library to a specific format (FLAC, MP3, or ALAC), regardless of the input format. This feature addresses the need for format consistency across audio collections and provides flexible conversion options.

✨ Features Added

🔧 Core Functionality

• New CLI Flag: --enforce-output-format with values: flac, mp3, alac
• Universal Conversion: Converts all supported input formats to the specified output format
• Intelligent Processing: Skips conversion for files already in the target format
• Metadata Preservation: Maintains tags and cover art through FFmpeg integration

🎵 Format Support Matrix

Input Format	Output Format	Conversion Method	Metadata Preserved
FLAC → MP3	SoX + FFmpeg	✅	✅
FLAC → ALAC	SoX + FFmpeg	✅	✅
MP3 → FLAC	SoX + FFmpeg	✅	✅
MP3 → ALAC	Copy (no conversion)	❌	N/A
ALAC → FLAC	FFmpeg + SoX	✅	✅
ALAC → MP3	SoX + FFmpeg	✅	✅

🎛️ Quality Settings

• MP3: 320 kbps CBR with appropriate sample rate (44.1kHz/48kHz)
• ALAC: 16-bit depth with smart sample rate handling
• FLAC: Maintains or reduces to 16-bit with optimal compression

🔧 Implementation Details

New Functions Added

• processAudioFileWithEnforcedFormat(): Main format enforcement logic
• processToMP3(): Handles conversion to MP3 format
• processToALAC(): Handles conversion to ALAC format
• convertToMP3(): SoX-based MP3 conversion with metadata preservation
• convertToALAC(): Two-step conversion (SoX→FLAC→ALAC) for optimal quality
• changeExtensionToMP3() / changeExtensionToM4A(): Utility functions

Enhanced Functions

• Updated processToFLAC() to support ALAC input
• Enhanced processAudioFile() to route through enforcement logic
• Improved Docker command structure for all conversion types

Validation & Error Handling

• Format validation with descriptive error messages
• Graceful fallback when metadata preservation fails
• Comprehensive input validation for supported formats

🧪 Testing Coverage

Coverage Improvements

• Overall Coverage: Improved from 74.3% to 76.4%
• New Test Functions: 12 comprehensive test suites added
• Key Function Coverage:
  • processAudioFileWithEnforcedFormat: 93.8%
  • processToFLAC: 84.2%
  • convertToALAC: 66.1%
  • processALAC: 49.1%

Test Categories

• ✅ Format enforcement validation
• ✅ Extension helper functions
• ✅ Conversion logic with various audio formats
• ✅ Docker mode compatibility
• ✅ Metadata preservation scenarios
• ✅ Error handling and edge cases
• ✅ Integration testing with real file operations

📝 Usage Examples

Command Line Usage

# Convert entire library to MP3
./lilt /path/to/music /path/to/target --enforce-output-format mp3

# Convert to FLAC for archival
./lilt /path/to/music /path/to/target --enforce-output-format flac

# Convert to ALAC for Apple ecosystem
./lilt /path/to/music /path/to/target --enforce-output-format alac

# Works with all existing flags
./lilt /path/to/music /path/to/target --enforce-output-format mp3 --use-docker --no-preserve-metadata

Behavior Examples

# Input: Mixed library (FLAC, MP3, ALAC)
# Command: --enforce-output-format mp3
# Result: All files converted to 320kbps MP3 with metadata

# Input: High-res FLAC collection
# Command: --enforce-output-format alac  
# Result: Converted to 16-bit ALAC with downsampling as needed

🚀 Technical Highlights

Advanced Conversion Pipeline

1. Quality Analysis: Examines source bit depth and sample rate
2. Smart Processing: Uses SoX for audio quality conversion
3. Metadata Preservation: Leverages FFmpeg for tag and artwork transfer
4. Format Optimization: Applies format-specific quality settings

Docker Integration

• Full compatibility with existing Docker workflows
• Proper volume mounting and entrypoint handling
• Consistent behavior across containerized and local environments

Performance Optimizations

• Skips unnecessary conversions for files already in target format
• Efficient two-step process for complex conversions (ALAC)
• Minimal temporary file usage with automatic cleanup

📊 Code Changes Summary

4 files changed, 1173 insertions(+), 16 deletions(-)

Development.md    |  35 +++++  (Documentation updates)
README.md         |  61 ++++++--  (Usage examples and flag documentation)
main.go           | 368 ++++++++++++++++++  (Core implementation)
main_test.go      | 725 +++++++++++++++++  (Comprehensive test suite)

🔍 Quality Assurance

Verification Steps

• ✅ All existing tests pass
• ✅ New functionality thoroughly tested
• ✅ Docker compatibility verified
• ✅ Metadata preservation confirmed
• ✅ Error handling validated
• ✅ Performance impact minimal

Compatibility

• ✅ Backward compatible with existing workflows
• ✅ Optional flag (no breaking changes)
• ✅ Consistent with existing CLI patterns
• ✅ Supports all existing audio formats

🎯 Benefits

For Users

• Standardization: Convert entire libraries to preferred format
• Flexibility: Choose optimal format for specific use cases
• Quality: Maintains high audio fidelity during conversion
• Convenience: Single command for bulk format conversion

For Developers

• Extensibility: Clean architecture for adding new formats
• Maintainability: Well-tested, documented code
• Reliability: Comprehensive error handling and validation

🔮 Future Enhancements

This implementation provides a solid foundation for future improvements:

• Additional format support (OGG, AAC, etc.)
• Custom quality presets
• Batch processing optimizations
• GUI integration capabilities

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Ready for Review ✅
All tests passing, documentation updated, and functionality verified across multiple scenarios.

[Copilot]

Pull Request Overview

This PR introduces a comprehensive --enforce-output-format feature that allows users to standardize their entire audio library to a specific format (FLAC, MP3, or ALAC). The feature provides intelligent conversion logic that avoids unnecessary re-encoding and preserves audio quality appropriately for each target format.

Key changes include:

• Added CLI flag --enforce-output-format with support for flac, mp3, and alac formats
• Implemented format-specific conversion functions with quality optimization
• Enhanced existing processing pipeline to route through enforcement logic when enabled

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
main.go	Core implementation of format enforcement with new conversion functions and CLI flag support
main_test.go	Comprehensive test suite covering all format enforcement scenarios and edge cases
README.md	Updated documentation with usage examples and format support matrix
Development.md	Technical documentation of the new feature implementation

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[Copilot]

Pull Request Overview

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

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