YouTube compresses the video as soon as it’s uploaded, so it’s unlikely you can obtain any sort of lossless download. You may be able to get a .wav or similar download of a video’s audio track, but there will still be compression losses from the YouTube side.
I think the idea of using coarse grounds for the French press is mostly for filtering out the grounds with the steel mesh on the plunger. If you have a finer mesh, by all means, go for it.
I’ve also seen some of my fellow coffee lovers at work use filters wrapped around their press, or using an ultra-fine metal mesh on their air press. They’ll go for a finer grind, and it definitely helps the brew steep quicker.
Personally, if I’m using a glass press, I can usually tell the brew is done by jostling the pot and seeing if the grounds sink. In my metal one, it’s usually 5+ mins, and then it’ll jostle and test the resistance with the plunger to see if the grounds sank.