Getting the line to show up clearly is a challenge. Old pics of casting demos were often shot at night using a bright line.
Charles Jardine had a special line that he used at demos which was fluorescent orange with alternating 12 inch black bars at 12 inch intervals. The visual effect was dramatic. I wonder if something like that might help with video analysis?
When sight fishing, look over your shoulder from time to time, you never know who's behind you