Back in 2009 the YouTube player had no quality switcher, but there was a trick: append &fmt=18 to any watch URL to force the higher-quality H.264 stream (and &fmt=22 for 720p where it existed). Same video, noticeably better audio and picture:
Normal quality / “High quality” (the 2009 way)
Does the trick still work?
No — the parameter is ignored today. It stopped mattering once YouTube moved to adaptive DASH streaming: instead of picking one pre-baked file via a URL parameter, the player now negotiates separate audio and video segments on the fly and matches the quality to your bandwidth. You control the result from the player’s gear menu (or let “Auto” do its thing), not from the address bar.
The video above is still up after all these years, so the links remain good for a nostalgia test — just don’t expect the fmt suffix to change anything.