One prompt: Claude builds a beat-reactive audio visualizer video end-to-end in its sandbox
vidiclol · reddit · 2026-09-28
A user uploaded a Guild Wars soundtrack remix to Claude.ai and asked for a beat-reactive glowing visualizer — Claude wrote and ran all the code in its sandbox and returned a finished 3.5-minute 720p MP4, rendered in 7 minutes on one core.
How Claude built it:
- Audio analysis: Python + librosa spectrogram, bass/mid/high band splits, HPSS for percussive onsets (120 BPM, 404 beats, 1,460 onsets).
- Not missing beats: took the peak value in each 33ms frame window instead of averaging, so transients survive; instant attack, smooth release.
- Rendering: Pillow layered frames — gradient sky, procedural mountains, sun/spectrum/ember layers, plus a bloom pass from blurred downscaled copies.
- Encoding: frames piped straight into ffmpeg with the original audio.
- Iteration: rendered a 5-second test, inspected still frames itself, and fixed two issues (back-ridge bleed-through, spectrum bars washing out) before the full render.
The standout detail: Claude chose peak sampling over frame averaging unprompted.
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