Flash vs disk

I recently played a 3.71GB movie on a DVD disk and then the same movie on a
4GB flash drive. All conditions were equal. Battery at 100%. The flash drive
lasted 1 hour & 35 minutes---the disk lasted 1 hour. I got an extra 35
minutes playing time with the flash drive. Unfortunately neither one lasted
for the full movie. I think that a 3.20Gb or less movie would go all the
way. I only had 10 more minutes to go with the flash drive. Are there any
suggestions how the play time can be stretched out. I have only had this
laptop (aspire 3680) a month and am still learning. I'm open to all
suggestions. Clint Email is ok, just make the subject "aspire" so I
don't delete it.