The problem is, you're describing Nero
Nero is NOT very forthcoming with what is REALLY being done, as they are more then happy to generalize things.
The first 4% usually "burn" really quickly, and then you have to wait a little bit for further progress right? what is really happening is Buffers are being filled, and the process is preparing to start, but nothing has actually been written to the disc yet.
Sometimes when I burn really REALLY small ISO's the bar fills up to 50% completed within 2-3 seconds, and then sits there for 20 seconds or so before continuing, and then waits another 20 seconds or so for the leadout. It makes perfect sense, but it LOOKS really weird!
Punch Cards -> Paper Tape -> Tape Drive -> 8" Floppy Diskette -> 5 1/4" Floppy Diskette -> 3 1/2" "Flippy" Diskette -> CD-R -> DVD±R -> BD-R
The Progression of Computer Media