C:\> play "Room for Another Way.mp3"
ready
SYNC MODE: press Space as each line begins, Backspace to undo, S to finish.
0:00 0:00
Space play or pause   ←→ seek 5 s   S sync lyrics by tapping   click any line to jump to it

Line start times in seconds, one entry per lyric line (null means unset). Copy this into const TIMES in index.html to make it permanent, or paste a list and apply it.