Help with burning iPhone 1080p video to a standard DVD disc.

I know it makes little sense these days to take a HD video and burn it to a standard DVD, but that is what I am trying to do and having a tough time. I am using Wondershare's Uniconverter to convert my 1080p video from my iPhone into a .vob format. I then burn the .vob file to a standard DVD disc. I totally realize that this makes no sense, but amuse me if you will. I am fully expecting , and I am OK with , the degradation of quality of the resulting video on the DVD -- HOWEVER, the videos go back and forth during playback where it gets super grainy and then back to regular grainy -- in very quick intervals (like every other second) , making it unwatchable.

So, my question is this: How do you take a 1080p video from an iPhone and convert it to a file format that will create a watchable DVD. Again, I know that the result will be SD -- I am Ok with that -- but without the intervals of super grainy/regular grainy. Any suggestions other than "don't even try" ? There has to be some video format that I can convert the 1080p to first that will make this work?