How to edit laying snow into a video?
EDIT: You need to be clear what your goal is. If this is a summer project and just something for some friends to work on together right now, I'd suggest getting Blender (https://www.blender.org/) and learning to use it together. Make some of your establishing shots, if you can.
Or start on a script. 99% of people with good ideas for a movie never make it because they never write and finish a script. Pick one scene and script it and shoot it. Do you need lighting? Props? Have you found a good location? Is it interesting.
Depending on your expectations, it will be very hard. But you can learn together and if things go well, you may have the foundation for actually making a movie.
Script-writing is hard. Movie shooting -- multiple angles, script, actors, props -- is hard. 3D (Blender) is hard. But if you're imagining that you can just run a camera and have people do what they want and in the end you make it look like it's winter -- that's VERY hard.
If it snows reliably in your area, you could easily take the next six months working on Blender, scripting, practicing some shots, scouting locations, etc in preparation for real snow. (Even if it doesn't snow, winter footage may be better than summer footage in terms of looking like winter.)
You can enjoy this process. But don't let your friends' expectations end up with lots of filming being done and then dumped on you to do the impossible. Make sure the process is iterative so your friends can see what's possible, rather than imagine a Hollywood budget.
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You'll really need to set expectations for your friends. A huge portion of the filming (say 98% or something like that) should be indoors.
Like most shows/movies you'll have an establishing shot of a snow-covered building in a snow-covered valley for a few seconds, then you'll cut to indoors scenes which you physically set up to plausibly look like they are the inside of that building we just saw the outside of. This establishing shot might be real video of a real building that really has snow, or you might attempt to take a photo and touch it up per some of the Photoshop tutorials, then animate falling snow or use a 3D program like Blender and animate a truck or something, so the still could be a video.
Inside, you might want to see the outside occasionally. Have the camera on a tripod and unmoving, looking at the scene with a window in the shot. To make it easy, don't have any people walk in front of the window. Make sure bright light is coming through the window, as if there were lots of snow outside. You can then figure out what it looks like outside of the window and replace the window with that image/video.
If actors walk in front of the window, you'd need to rotoscope around them -- hard -- or the window would need to be a greenscreen or something like that -- also hard -- so you could have the actor appear in front of your replacement window view.
Better yet, fake it. The snow is so high or the wind is so strong that snow/ice cover the windows and you can't see out. Pile fake snow in a bag against the outside of the windows. Every aspect of the script will have to be driven by whether you can actually pull off the shot or not.
Do some experimentation first to see how realistic you get, before you write a script and get actors and crew and actually spend days taping. Your friends can fantasize about how it will look, but you'll be on the hook to fulfill their dreams and it's absolutely not easy.
Anyhow, if your video editing software has color grading/correction tools you can try to do what the Photoshop tutorial does: pick areas of your frame that are green or bright and tint them very white -- leaving some light/darkness variation so it looks a bit more 3D. I tried that really quickly on a scene and the best I could do is to have it look like a dusting of snow had fallen on some grass. And there was a lot of flicker in the color: it's easy to get a single still frame looking good, but video has noise and the light is changing from frame to frame, so it's easy to get flickering when you're doing as extreme of a color adjustment as making stuff look white.
But it's not going to look like the North Pole. There's another Photoshop Tutorial that I see recommended from the end of the one you linked. It uses an old wood cabin and the thumbnail shows a before/after split screen. Notice that they replace entire chunks of the image with white, then add shading and texture to give it depth. That's what a real movie would do in your case: most of the outdoor scenes -- basically anything that your actors don't touch -- would be masked out and replaced by 3D renderedings.
So it's in your best interest to have pretty much everything take place indoors (in a building, in a cave, etc), with some peeks at the outside.