Not necessarily. The stars don't have to be exactly 20% each. You could make 1 star 10%, 2 stars 25%, 3 stars 50%, 4 stars 75% and 5 stars 100% and then you could also include the option for a slider scale that would do a rounding estimate of all the votes (both sliding votes and stars) and display the mean rating in stars. So that would allow people to be specific with their votes, but also allow for a quick way for people to judge if they should watch the video based on the stars.
I personally think people should flag more often and not get offended by them. To me a flag means I'm not doing the best I could be and I didn't reach my potential with the post.