[Movie/video] DVD burning issues

              When I try to use an application, like k3b, DeVeDe, or anything else like that, either it won't burn my .avi movies into a disk, or it will load while converting, and stop about 80% of the way to being finished. I have been patient, and have even left it to load for 10 hours, and it won't move anymore, it is stalled.
             So I tried instead to burn a DVD with the command line, by creating an .iso with the files, and burning it to the DVD. This is much faster. It worked successfully with an episode of a TV show, but when I try to make a full-length movie (I tried two different ones, and I am sick of wasting DVDs) it only makes the first 18 minutes, then the DVD just stops, it's over. These are the commands I am using,

ffmpeg -i ELF.avi -target ntsc-dvd foo.mpg

#2 Build the file structure.
Code:
dvdauthor -o DVD/ -t foo.mpg && dvdauthor -o DVD/ -T
(Creates a folder named DVD)

#3 Make an iso.
Code:
mkisofs -dvd-video -v -o DVD.iso DVD
(Creates a file named DVD.iso)

And then I burn it, and it is just the first 18 minutes, even though the file itself is complete, as well as the foo.mpg file when previewed.
If anyone could help please, that would be great! I really would like to burn these movies, my family would enjoy them. (Elf and A Christmas Story)