MediaRecorder in Electron 33 muxes MP4 with avc1 High profile + AAC; on macOS that encode runs on VideoToolbox hardware, whose realtime quality ceiling is far above software VP9 — the residual smearing came from there. Bitrate cap raised to 50 Mbps (hardware barely notices; the VP9 fallback undershoots regardless). ffmpeg sniffs containers by content, so the .webm temp name keeps working. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XVMQ2JhsJ77pGKqcvvFHqc