- compose-widescreen: ambient bed was 0:88 but narration runs ~2:56, so music dropped out halfway. Loop the bed (-stream_loop -1), trim to runtime, add in/out fades so it carries the whole piece. - render-progress heartbeats wired into captions-train, opener-anim, and the compose main encode + opener-join (ffmpeg frame= parsing) so long widescreen renders show a live Slab menubar bar like /pop video renders do. - youtube-description.txt for the unlisted share cut (youtu.be/nUxW8mCzv-E). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>