Never tried it with iTunes, but I use DVDVideoSoft for alot of converting/burning. M4V is listed as a compatible input format so it should work. Although im not sure about the copy protection iTunes uses. Free software though, worth a try. http://www.dvdvideosoft.com/products/dvd/Free-MP4-Video-Converter.htm
Edit: Also handbrake is a great opensource tool for converting, although i dont believe you can burn to dvd's https://handbrake.fr/