When you’re burning a CD or DVD, the computer isn’t typically the weakest link; it’s the CD/DVD burner. When they write, CD/DVD burners operate at some maximum speed of rotation and how quickly a burner spins depends on its hardware and how fast it can write the data to that disc.
But I think something else might be going on here. You mentioned that your original video is in MP4 format. That’s not a format that is written to DVD.