Rewind and Forward by 5 seconds
Because Rakuten Viki puts a certain amount of focus on those who are learning languages (e.g. Learn Mode - although this doesn't seem to work on most Japanese shows/movies), I think it would make sense to allow users to rewind/forward in smaller increments than 10 seconds. E.g. when I want to hear a sentence a second time for learning purposes I would like to be able to rewind no more than 5 seconds.