Four Prompts, Five Minutes: Codex Composes a Concerto with Scores, Animation, and Real Instruments
mhmazur · x · 2026-09-06
The author told Codex (with GPT-6 Astra) to "compose a concerto" and got "Lanterns at the Water," a three-movement miniature concerto for piano and strings, in five minutes over four short prompts.
- Scores: MIDI, editable MusicXML, and a synthesized audio preview.
- Visualization: An agent-written Python renderer reads the score — piano notes become floating lanterns (pitch sets horizontal position), sustained strings shape rippling water — drawn frame by frame with Pillow/NumPy and encoded to 720p via FFmpeg.
- Real instruments: To replace MIDI sound, it found Apple's built-in instrument bank and wrote a Swift renderer using AVAudioEngine with sampled piano, strings, and cello, adding stereo placement and hall reverb.
- Final sync: FFmpeg swapped in the new soundtrack without re-encoding visuals.
A representative end-to-end agent demo: scores → animation → real audio → final mux, fully reproducible.
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