Hello, can I donwload a video from youtube and put it in a mobile app? (app is free and there is no video on the page that can make it monetizable)
you should create your own content to avoid problems using the video.
Unless the video states it can be used for redistribution of content or is allowed for royalty-free commercial usage- don't.
If you're looking for video content that supports your brand or platform idea directly, you're far better off creating the content yourself.
Imagine what size will be your app if you fit there a few short videos (no matter if it's small size files)
If you really want to download videos from YouTube, open your Mozilla-Firefox, --> add-ons --> extensions --> look for YouTube downloader