There's a great choice of formats both video and audio including MP4 and MP3. You can download captions for individual videos, and there's support for 3D and 360-degree videos too.
I don't get the point of this post. What exactly do you want from us? To use 4K video downloader -- (does this site even exist? A quick google search turns up nothing.)
Or to use your site, which looks like youtube, but the state it was in roughly 7 years ago. Besides that, your site doesn't allow for a quality higher than 720p30?
I'm pretty sure sites like
https://streamable.com/ offer better resolutions, and look cleaner/are more established as well..