Google is now throttling what it detects as youtube-dl clients to ~50% of playback speed (no matter what resolution). nbd for archiving, but it wrecks the mpv integration. There is a fork, "yt-dlp", that includes (among a number of other amenities that the upstream devs are slow or hesistant to merge) a fix for this, and its authors have expressed intent to track upstream to avoid the fate of its spiritual predecessor, yt-dlc.