🎧 Audible Metadata Integration

This release adds comprehensive Audible metadata integration, allowing automatic enrichment of audiobooks with professional metadata from Audible's catalog.

✨ New Features

Audible Metadata Features

• New metadata command - Fetch and manage Audible metadata
  • metadata fetch - Query Audible by ASIN or title/author search
  • metadata enrich - Inject Audible metadata into existing M4B files
• Build integration - Automatic metadata fetching during conversion
  • --fetch-audible - Enable Audible metadata enrichment
  • --audible-region <REGION> - Specify Audible region (us, uk, ca, au, fr, de, jp, it, in, es)
  • --audible-auto-match - Auto-match books by folder name
• ASIN auto-detection - Automatically detects ASINs in folder names
  • Pattern: `Book Title [B00G3L6JMS]`
  • Supports multiple formats: brackets, dashes, standalone
• 10 Regional stores - Full support for all Audible regions
  • US, CA, UK, AU, FR, DE, JP, IT, IN, ES
  • Region-specific catalog access

Metadata Extraction

• Comprehensive fields extracted from Audible:
  • Core: title, subtitle, authors (with ASINs), narrators, publisher, year
  • Content: description, language, duration, abridged status
  • Organization: series (with sequence numbers), genres, tags
  • Identifiers: ASIN, ISBN
  • Media: cover URL, customer rating
• Cover art download - High-resolution cover artwork
  • Automatic download and embedding
  • Replaces local covers with Audible artwork
  • Configurable via `metadata.audible.download_covers`

Caching & Performance

• Filesystem caching - Intelligent metadata caching
  • Location: `~/.cache/audiobook-forge/audible/`
  • Default TTL: 7 days (configurable)
  • JSON format for easy debugging
  • Automatic cache expiry based on file modification time
• Rate limiting - Respects Audnexus API limits
  • 100 requests per minute (token bucket algorithm)
  • Automatic wait when limit approached
  • Configurable via `metadata.audible.rate_limit_per_minute`

Configuration

New `metadata.audible` config section:
```yaml
metadata:
audible:
enabled: false # Auto-fetch during build
region: "us" # Default region
auto_match: false # Search by folder name
download_covers: true # Download cover art
cache_duration_hours: 168 # 7-day cache
rate_limit_per_minute: 100 # API rate limit
```

📖 Usage Examples

Fetch Metadata by ASIN

```bash
audiobook-forge metadata fetch --asin B00B5HZGUG --region us
```

Search by Title/Author

```bash
audiobook-forge metadata fetch \
--title "The Martian" \
--author "Andy Weir" \
--region us \
--output metadata.json
```

Enrich Existing M4B

```bash

With explicit ASIN

audiobook-forge metadata enrich --file book.m4b --asin B00B5HZGUG

Auto-detect ASIN from filename

audiobook-forge metadata enrich \
--file "The Martian [B00B5HZGUG].m4b" \
--auto-detect
```

Auto-Fetch During Build

```bash

With ASIN in folder names

audiobook-forge build \
--root /audiobooks \
--fetch-audible \
--audible-region us

Auto-match by folder name

audiobook-forge build \
--root /audiobooks \
--fetch-audible \
--audible-auto-match
```

🔧 Technical Details

New Dependencies

• `reqwest` (0.11) - HTTP client for API calls
• `governor` (0.6) - Token bucket rate limiting
• `lazy_static` (1.4) - Regex compilation optimization

Files Added

• `src/models/audible.rs` - Data structures for Audible metadata
• `src/audio/audible.rs` - HTTP client and API integration (399 lines)
• `src/utils/cache.rs` - Filesystem caching layer (219 lines)
• `tests/audible_integration.rs` - Integration tests
• `AUDIBLE_METADATA.md` - Comprehensive feature documentation (387 lines)

API Integration

• Audnexus API - https://api.audnex.us
  • Public API (no authentication required)
  • Community-maintained wrapper around Audible
  • Endpoints:
    • `GET /books/{ASIN}?region={region}` - Fetch by ASIN
    • `GET /books?title={title}&author={author}` - Search

Code Statistics

• ~1,500 lines of new code
• 100% test coverage for core functionality
• Zero compilation errors
• Full async/await integration with existing Tokio runtime
• All 81 tests passing

📚 Documentation

See AUDIBLE_METADATA.md for comprehensive documentation including:

• Quick start guide
• Configuration options
• ASIN detection patterns
• Regional support details
• Troubleshooting guide
• API reference

🚀 Migration Notes

Enable Audible Metadata

1. Update to v2.2.0:
   ```bash
   cargo install audiobook-forge --force
   ```

2. Initialize/update config:
   ```bash
   audiobook-forge config init --force
   ```

3. Enable in config (optional):
   ```yaml
   metadata:
   audible:
   enabled: true
   region: "us"
   ```

4. Use during build:
   ```bash
   audiobook-forge build --root /audiobooks --fetch-audible
   ```

ASIN Folder Naming

For automatic detection, rename folders to include ASINs:
```bash

Before

My Audiobook/

After (ASIN auto-detected)

My Audiobook [B00G3L6JMS]/

or

B00G3L6JMS - My Audiobook/
```

⚠️ Limitations

• API rate limit: 100 requests per minute (Audnexus restriction)
• Auto-match accuracy: May have false positives with common titles
• Region-specific: Books must be available in selected Audible region
• Network required: Metadata fetching requires internet connection

🔮 Future Enhancements

Potential improvements for future versions:

• Interactive search result selection
• Batch metadata updates for existing M4B libraries
• Custom metadata field mapping
• Integration with other metadata sources (MusicBrainz, GoodReads)
• Metadata comparison and conflict resolution UI

Full Changelog: https://github.com/juanra/audiobook-forge/blob/main/CHANGELOG.md