Thick timeline with hatched cache range, chapter diamonds and chapter/time hover boxes; collapses to a thin progress line when hidden. Flat icon row with track count badges, shader preset badge, flat dark menus. Own show/hide state, live switch in window and fullscreen. New buffered signal from demuxer-cache-time. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>