for the video slice: a user cant like and dislike a video, correct? so i really like the idea, but maybe we can instead have a key that says something like emotion: that can have values of 'like', 'dislike', or false? Maybe a different key to make it sound better... Otherwise, looks great!
comments slice should have a parentCommentId and maybe same thing for likes/dislikes
when you put the timeElapsed does that mean that your going to have to send an action every second? that might be too much... if we refresh the page, i guess the user will lose where they're at... too bad. :)
Everything else looks awesome! Really good job!