Automatically drawing hint lines has been a request from a few people. When I talk to personal trainers or athletes (new or serious) in various sports, I've tested out this concept by asking them what they'd want drawn. Turns out, it's so contextual, opinionated and subjective, I don't think there's a great approach unless I assume we have an unrealistic amount of context.

e.g., one case is kettlebell swings. You might want to see how consistent your swings are in a set, and between sets. To do this well, you'd need to reliably detect the kettlebell swing exercise using some N-way classifier. And then, correct for camera position. And then, center the relevant part of the body (is this shoulder? hips? turns out people have different opinions).

Instead, we're going to use a more generic visualization approach that doesn't try to be opinionated. But, I'm expecting to open-source the visualization front-end so it's tweakable by users.