Combining two videos in this way would be unlawful in the UK, where we have the very restricted "Fair Dealing" concessions, because downloading the videos in the first place is a tort[0].
Combining them is another, sharing them is another.
We basically have no concept of personal use in our copyright.
[0] if they were broadcast you can record but only for time-shifting, you can only watch once (alone!) and then are obliged to destroy the copy; you aren't allowed to format shift.
The lack of any remaining semblance of balance in copyright between the rights of the demos and media interests shows how badly distorted our Western democracies have become from representing the rights of people in general above the rights of the rich.