I use a tool called Slush Puppy's Retime Tool which you can find Here: https://github.com/Slush0Puppy/retime This tool allows me to Re-time runs directly from youtube. Here's the user interface:

1. Get the Video FPS from left click on the video --> nerd stats:

2. Advance or go back frame by frame with the keys "." and "," to catch the first and last frame of the run.
   Left click --> Copy debug info --> Past respectively on Start Frame and End Frame

FIRST FRAME OF THE RUN / LEVEL : It's the first frame you see the white bar and the viewfinder.

LAST FRAME OF THE RUN / LEVEL : It's the first frame you see the orange exagon coming out from the hole.

3. Don't touch the Modifier and get the final time: