Auto-generating YouTube thumbnails with ffmpeg inside a CI pipeline

When I started auto-publishing YouTube videos from GitHub Actions, the default thumbnails were whatever frame YouTube chose to freeze on. Usually a half-rendered slide or a moment of black. They looked unprofessional enough that I fixed it before worrying about anything else. The result is thumbnail.sh — 51 lines of bash that run as step 4a in my publish pipeline, generate a 1280×720 JPEG from the finished mp4, and hand it to upload.py for thumbnails.set . Here's how it works and where it's stil