It's a bug in Audience and it's already reported on Launchpad: https://bugs.launchpad.net/audience/+bug/1362910
P.S. If you've wandered to this post and saw this bug, and it affects you - please click "this bug affects me" on a launchpad to let developers know about the IPU
That has nothing to do with your graphics card. Are you sure the file you are trying to play has subtitles? Or are you trying to open a subtitle file?
Also, if you have your graphics drivers correctly installed you should have a NVIDIA X Server Settings icon in your Applications menu. The correct console command is nvidia-settings.