What was wrong with the old trailer you may ask?
First off, I was editing video that was compressed (H.264). This is a great codec for sharing/streaming - but it is too compressed to edit. I had to go back to my original file for the short film which was in Apple Pro-Res 422 and re-edit that (tons of fun).
I also wanted to fix the end title design. I knew it wasn't perfect because I basically just swapped it in from the short film. The problem with that is that the short film doesn't have a title come up. I go from a riddle down to the title (barely) - to a title card stating 'Year 4' at the front. Karol made a comment and he was right - it didn't work. So I had to create a title card that had 4 come up, then 2, then 3. This is actually when I discovered my codec problem. So, a fix that should have taken a day took about two weeks.
But now the resolution is much higher (it may be imperceptible, but the colors are brighter, the blacks are darker and the images are sharper) - and I have a much better title design.