Watching this makes me feel Joy and Sadness all at the same time.
That is a weird combination. It's like eating a Salty, and Sweet, piece of Pizza, and not hating that, or putting Hot Sauce, (which I love) on Ice cream, which I also love. You just never think of mixing those flavors and yet here is a mix of flavors for your eyes. - Your Eyes and your emotions are just more advanced than your taste-buds. They can process the contradictions inherent in the visual.
Overall, I realize the Joy in watching this truly out-weighs the underlying sadness, otherwise you really could not stand it. I have watched it about ten times, and each time it makes me cry. I honestly don't want to watch it enough where I don't.