The realtime VP9 first pass at 12 Mbps was the bottleneck on full-screen abstract motion (visible blocking the MP4 pass could not recover), and the x264 pass added its own loss at CRF 20 veryfast. The WebM intermediate is deleted after muxing, so it can afford 30 Mbps; the MP4 pass is offline, so it can afford CRF 18 preset medium, constant 30 fps and 256k AAC. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XVMQ2JhsJ77pGKqcvvFHqc