I don't know the exact technique, but you're supposed to record a lag-free TV, with your controller in the picture as well.
Then you do the move and measure it on a computer after you've finished recording... like I said, I don't know the details.
If you have correct frame data it's easier to compare moves to find out frames. i.e., you make the other character block a move that leaves you on 0 frames, then you do the desired move and you see what it trades with or gets beat by, and you guess from there.