Roll out is when the ball uses all it's energy too early.  It is not necessarily a bad thing if you can use it properly, but you do tend to sacrifice some hit.  It can be caused be a lot of things, all of which will be accentuated by low ball speed.  In the video, I'd say it's mostly release (she's pretty up the back) and drilling (you can drill the ball to use it's energy faster or slower).  Faster speed or more axis rotation could be solutions.  Another common cause is too much surface for the condition.