Is there a way you can resume renderings with cycles in AVI JPEG Format? Like if you wanted to stop your computer and give it a break and then start off the next time where you ended it? I don't know, it's just a question I've been asking my self a long time
To do the rendering in different sessions, render as an image sequence first. Make sure you disable the Overwrite option on the render output, that way the frames that are already rendered will be unaffected, no need to change the start point.
Once you are finished rendering all of the frames of your scene compile the image sequence into a video format.