I want to make an underwater shot where someone falls slowly with bubbles and on their back under water like this footage. Any tips or tutorials on how to do that ?
Honestly I'd say get a waterproof case for your camera and shoot in a pool. Otherwise you'll have to deal with much more than bubbles, but the way hair and clothing is caught.
Modeling things like hair and clothing underwater is beyond the scope of Hitfilm... That's getting into full-on simulation (at which point you may as well sim the bubbles) in a dedicated 3D app.
Bubbles are the EASY part.
Still, for bubbles your two choices are the particle sim (costs money) or Blood Spatter. Blood Spatter can be modified to generate white or light blue orbs that rise to the top of the screen. Somewhere I have a quick project I threw together for someone else who wanted to make underwater bubbles. Next time I'm on my computer I'll look for it.
To do this practically (if your talent is willing), buy/rent a harness for your talent, and suspend them upside down in front of a black screen (you could use a blue/green screen, but if you want a dark background for the final, black might be easier to work with in the long run). Shoot at a high frame rate, and have a fan above them blowing down to add some billowing to hair and clothing. Mask out whatever they're hanging from, flip the footage 180 degrees, then add the bubbles.
NOTE: Hanging someone from their waist like this gets into safety issues, so this should ONLY be done with the help of someone who knows what they're doing. Maybe find a local rock climbing group and enlist the help of an experienced climber who can work with you to find a good harness that will support the talent's weight safely. You'll also need to build some kind of rig to suspend this person, or find a facility with suitable equipment. In short, be wise if you take this approach.
@Triem23 @CleverTagline thank you guys. i am planning to do it in real life with water proofing case. my question is do i need to shoot on high frames and do i need much lighting. and whether i can film at day and change it later in post as night
@arcfilm I can tell you from my recent experiments with an ActionCam in a 14 foot outdoor aboveground pool with my grandkids that lighting is crucial. On an overcast day, the water appeared murky as lake water, but as soon as the sun came out it was crystal clear. It takes a lot of light to shoot underwater if you want clear footage. To accomplish what you show in the video a larger pool is very important so you can use a maybe a single directional light on the figure but the walls in the distance will be dark and invisible...unless you can find a way to paint them green. I toyed with the idea of making some green plywood inserts that I could lower into the pool but never progressed that far. Anyway, that's been my experience with underwater shooting. Here is some test footage I did:
You can tell by the caustics this was an mostly bright sunny day and the water was actually crystal clear but the farther from the camera the murkier it appears. It takes a look of light in the water.