Dont worry about formats. I think 70% editors have problem with that.
there are 2 ways for handling formats.
1) using convertor programs which convert m4v to avi
2) changing the extention of the file (for example if u go to my computer and its sample.m4v change it to sample.avi )
about dvd i should say some editing programms like Edius captur dvd directly.
I hope it helps.