GPT-6 Astra Ultra built a 2-minute Blender/MIDI music video from one prompt: workflow and checks

This is my production experiment. I gave GPT-6 Astra Ultra one 2,778-word production prompt (~3K), then let it run for about four hours with no follow-up steering. It delivered Leave a Way, a two-minute Eurodance song and Blender video about a folding ruler becoming a bridge for a stranded bead. The interesting implementation choice was to make editable artifacts with code and existing assets. There was no Suno, Midjourney or Sora. The music was explicitly scored at 128 BPM using MIDI, conventional synthesis/DSP and seven drum, piano and Foley samples. The visuals came from scripted Blender scenes: an eight-leaf folding mechanism, a bead, a broken track and timed in-world lyrics, with workshop props from asset packs. The agent iterated within the run. It removed drums and bass for six bars at the story's decision point, corrected intersecting geometry, adjusted the portrait camera and aligned lyric visibility with the sung phonemes. “One-shot” means one initial instruction from me; it does not mean the agent made only one attempt. It also wrote checks for vocal pitch/timing, clipping and loudness, stem reconstruction, text framing, contact clearance and video decoding. Both local exports are 120 seconds / 3,600 frames, with identical soundtracks. These checks establish technical properties; they do not measure musical taste or storytelling quality. AI disclosure: local Hoshino Hanami/DiffSinger by Lotte V supplied the singing; Gemma 3 1B and Llama 3 8B supplied brainstorming drafts. The system had existing tools and asset libraries, so this is one production example, not a blank-machine benchmark or a controlled model comparison. A useful design choice was specifying editable deliverables and checkable constraints up front. The run produced Blender scenes, MIDI, stems and source scripts as well as the final videos, making individual decisions inspectable. Demo (2 minutes): https://www.youtube.com/watch?v=WUztyIXQpik Asset credits: CarpentersWorkshop; JustBStudios 1850sPostOffice; Ableton, Audentity Records and Dome of Doom samples; Fira Sans. Full credits accompany the demo. This write-up was prepared and posted by my AI assistant with my authorization.