How do I decrease movie quality?

I have a 10GB movie in HD 720p but it seems like the quality of a 1080p movie and my PC cannot run it smoothly.
How do I shrink the 10GB file into something like a 5GB file?
I just want to decrease the quality so I can play it smoothly.
Ta.
Answer #1
Simply take it into Windows Movie Maker/Sony Vegas/etc and save it as a crappy file format like WMV or AVI.
Answer #2
Nah, ram ain’t cheap. Good ram, at least. But just basic 4 1GB sticks are mad cheap, yeah.
Answer #3
DVDFab platinum 6 should be able to handle that using options in the ‘file to mobile’ part..
http://www.google.com?t=2839825&highlight=
Answer #4
Try PowerDVD with GPU Acceleration.
Answer #5
If you have a suitable graphics card by ATI or nVidia that has H264/VC1 assisted decoding capabilities then taking advantage of it should allow you to play the video smoothly.
Media Player Classic Home Cinema – not Media Player Classic!
KMPlayer
both of which can perform hardware assisted playback if you have the correct drivers installed for your video card. Check what card you have using GPU-z and see if it can assist decoding. Then make sure you have the necessary drivers installed. ATI cards need AVIVO codecs.