How can I download video from Youtube and Twitter

[luongwd]

I'm wondering if there is an app available on AppStore for this purpose. Or is there any method I can take to have this kind of app on my iPhone?

I did search on Google for some apps, but none of them works as the descriptions. I also read tutorials I found about this problem (like this) but it's kind of complicated as so many steps are required. I'm looking for an easier method. Please help me if you know a better solution.