The lack of an iMovie application in Ubuntu is one of the serious problems with the distribution. It makes us look like amateurs which is why news that PiTivi is going to be included by default is good news, at least in terms of driving development around video editors.
Here is a nice edition to any video applet collection. Photofilmstrip turns collections of images into movies. Doesn’t appear to be any way of adding a soundtrack, but that is easily accomplished by importing into PiTivi, Kdenlive or Lives.