[rpigab]

Well, obviously, APIs provided by Google can allow app creators to do many things, but not things that are useful. Only Google apps can do useful things, per Google policy.

See this SO answer https://stackoverflow.com/a/8081778/12405367

"Downloading Youtube videos is against their Terms of Service, so their API's will not support that."

Downloading videos for streaming services makes them cry, Not only Google, Netflix also hates people who go off the grid too. You should be online at all times and feed them data and money, and save your credit card details in-app, ready for compulsive buying. One day you'll be able to buy things while you sleep.