graph TD A[Start] --> B[Receive MP3 URL Input] B --> C[Validate MP3 URL] C --> D{URL Valid?} D -->|No| E[Return Error] D -->|Yes| F[Process MP3 with Source Separation] F --> G[Generate Vocal Stem] F --> H[Generate Instrumental Stem] G --> I[Create Vocal MP3 URL] H --> J[Create Instrumental MP3 URL] I --> K[Combine URLs into Output Array] J --> K K --> L[Return vocal-and-instrumental-stems] L --> M[End] E --> M