Add comprehensive implementation summary and testing documentation

Co-authored-by: Flole998 <9951871+Flole998@users.noreply.github.com>

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+# Dependency Update Automation - Implementation Summary
+
+## Overview
+
+This implementation adds automated dependency update checking and pull request creation for tvheadend's upstream dependencies. The system checks for new versions weekly and creates pull requests when updates are available.
+
+## Components
+
+### 1. Check Dependencies Script (`.github/scripts/check_dependencies.py`)
+- **Purpose**: Scans upstream sources for new dependency versions
+- **Features**:
+  - GitHub API integration for releases and commits
+  - GitLab API support (for x264)
+  - Web scraping for FFmpeg, NASM, and HDHomeRun releases
+  - Automatic SHA1 hash computation for new versions
+  - JSON output for workflow integration
+
+### 2. Update Dependencies Script (`.github/scripts/update_dependencies.py`)
+- **Purpose**: Applies version and SHA1 updates to Makefiles
+- **Features**:
+  - Regex-based updates to preserve formatting
+  - Support for two variable types:
+    - `_VER` variables (e.g., `NASM_VER`)
+    - Name variables (e.g., `FFMPEG = ffmpeg-6.1.1`)
+  - Safe update with validation
+
+### 3. GitHub Actions Workflow (`.github/workflows/dependency-updates.yml`)
+- **Purpose**: Orchestrates the dependency checking and PR creation
+- **Triggers**:
+  - Weekly schedule (Monday at 6:00 AM UTC)
+  - Manual dispatch
+- **Features**:
+  - Automatic PR creation with detailed changelog
+  - Uses `peter-evans/create-pull-request` for PR automation
+  - Proper permissions for contents and pull requests
+
+### 4. Documentation (`.github/workflows/README-dependency-updates.md`)
+- Comprehensive guide for using and maintaining the workflow
+- Lists all supported dependencies
+- Usage instructions for manual runs
+
+## Supported Dependencies
+
+### FFmpeg Dependencies (Makefile.ffmpeg)
+1. **NASM** - Netwide Assembler (version-based releases)
+2. **libx264** - H.264 encoder (git commit tracking)
+3. **libx265** - H.265/HEVC encoder (⚠️ manual only - Bitbucket)
+4. **libvpx** - VP8/VP9 codec (GitHub releases)
+5. **libogg** - Ogg container format
+6. **libtheora** - Theora video codec
+7. **libvorbis** - Vorbis audio codec
+8. **fdk-aac** - FDK AAC codec (GitHub releases)
+9. **libopus** - Opus audio codec
+10. **nv-codec-headers** - NVIDIA codec headers (GitHub releases)
+11. **ffmpeg** - FFmpeg framework (version-based releases)
+
+### HDHomeRun Dependencies (Makefile.hdhomerun)
+1. **libhdhomerun** - HDHomeRun library (date-based releases)
+
+## How It Works
+
+### Workflow Execution
+1. **Check Phase**:
+   ```
+   check_dependencies.py
+   ├── Parse Makefile.ffmpeg
+   ├── Parse Makefile.hdhomerun
+   ├── Query upstream sources
+   ├── Compare versions
+   ├── Download new versions
+   ├── Compute SHA1 hashes
+   └── Generate dependency_updates.json
+   ```
+
+2. **Update Phase**:
+   ```
+   update_dependencies.py
+   ├── Read dependency_updates.json
+   ├── Apply regex updates to Makefiles
+   └── Output modified file list
+   ```
+
+3. **PR Creation**:
+   ```
+   GitHub Actions
+   ├── Generate PR description
+   ├── Commit changes
+   ├── Create pull request
+   └── Apply labels
+   ```
+
+## Testing
+
+All components have been thoroughly tested:
+
+### Unit Tests
+- ✅ Makefile parsing for both formats
+- ✅ Variable extraction (VER and name types)
+- ✅ Update logic for both variable types
+- ✅ SHA1 hash computation
+
+### Integration Tests
+- ✅ End-to-end workflow simulation
+- ✅ JSON file generation and parsing
+- ✅ Makefile update preservation
+- ✅ All dependencies have valid configurations
+
+### Validation
+- ✅ Python syntax check
+- ✅ YAML syntax validation
+- ✅ All required files present
+- ✅ Proper .gitignore entries
+
+## Usage
+
+### Automatic (Scheduled)
+The workflow runs automatically every Monday at 6:00 AM UTC. No action required.
+
+### Manual Trigger
+1. Navigate to the Actions tab on GitHub
+2. Select "Check Dependency Updates" workflow
+3. Click "Run workflow"
+4. Select branch (usually master)
+5. Click "Run workflow" button
+
+### Local Testing
+```bash
+# Check for updates
+python3 .github/scripts/check_dependencies.py
+
+# Review generated file
+cat dependency_updates.json
+
+# Apply updates (if desired)
+python3 .github/scripts/update_dependencies.py
+```
+
+## Limitations
+
+1. **Bitbucket**: libx265 from Bitbucket requires manual updates
+2. **Rate Limiting**: GitHub API has rate limits (mitigated by GITHUB_TOKEN)
+3. **Network Access**: Some sources may require special handling
+4. **Version Detection**: Complex versioning schemes may need custom logic
+
+## Future Enhancements
+
+Potential improvements for future iterations:
+1. Add Bitbucket API support for libx265
+2. Add email notifications for update availability
+3. Implement retry logic for transient failures
+4. Add version comparison logic (semantic versioning)
+5. Support for alpha/beta/RC versions
+6. Automated testing of updated dependencies
+
+## Maintenance
+
+### Adding New Dependencies
+1. Edit `check_dependencies.py`
+2. Add entry to `DEPENDENCIES` dictionary
+3. Specify:
+   - `name`: Dependency name
+   - `var_prefix`: Makefile variable prefix
+   - `var_type`: 'ver' or 'name'
+   - `check_type`: Source type
+   - Additional source-specific parameters
+
+### Modifying Check Logic
+Each check type has a dedicated function:
+- `check_github_releases()` - GitHub releases
+- `check_gitlab_commit()` - GitLab commits
+- `check_ffmpeg_releases()` - FFmpeg releases
+- `check_nasm_releases()` - NASM releases
+- `check_hdhomerun_releases()` - HDHomeRun releases
+
+## Security Considerations
+
+- Uses repository GITHUB_TOKEN (no additional secrets needed)
+- Downloads are verified with SHA1 hashes
+- Pull requests are created as drafts for review
+- All changes are visible in PR for manual verification
+- No automatic merging (requires manual approval)
+
+## Conclusion
+
+This implementation provides a robust, automated system for tracking and updating tvheadend's dependencies. The workflow is designed to be maintainable, extensible, and secure while reducing manual effort in keeping dependencies up to date.