Farming

[Toxcatl]

I've read about this method for Android here on the forum:
Settings -> Google -> Ads -> Reset advertising ID
I haven't tried it though, maybe it's just a rain dance.

The number of videos available varies, yes.

If you do too much farming, then the supply of videos for you may dry up completely for a day or two...

Never happened to me. Availability is a local thing, but I seriously doubt it has such a long-term effect. I've never heard about it, and never experienced it. Not just every day is completely separate, but during the day situation may change: at one moment there are only 10 videos, in a couple of hours 15 more.

If you need to use greens to get the condition of your players back up to maximum, consider using the free video for each player via the training menu. I use this all the time (you have to make sure you can complete it before your match). I don't need to farm and the supply of videos stays at a high level.

These videos are from the same pool. If there are no videos available, they are unavailable everywhere, and vice versa -- if you can watch a video to restore player's 15%, you can watch it to get 1 rest pack. It is always like this to me, no matter if videos are plenty or scarce.