Takes start and stop points of a YouTube video, down to the frame, and gives the time between them in the format 1h 23m 45s 678ms. Source code is available.
Right click the YouTube video and select “Stats for nerds.” The third line is “Current / Optimal Res” - find the two numbers after the @ and enter them for framerate.
Find the starting point (you can use the , and . keys to find the exact frame). Right click the video and select “Copy debug info” and paste it for starting frame. Repeat for ending frame.