I use video and still photos a lot. I use a transparent grid over my monitor and often view action in both slow motion (one fifth speed is great) and frame by frame. It is easy to see what is happening when. The grid shows immediately if someone's center is going up or down, etc.
Students that are a long distance away send me video with questions and examples of their training and we can then film an answer that may help.
"One picture is worth a thousand words." Some wise old Chinese guy supposedly said that some time ago.