The past couple of days I have been downloading big avi and mkv files on my primary SSD drive. Afterwards, I convert them to mp4 files. I then add them to my iTunes library which then gets copied over to another separate hard drive on my MBP. After this, I delete both the files on my primary drive and empty the trash, however the free space indicator hardly moves. I just deleted over 10GB and it moves about 2-3GB. Sometimes when I do a mass delete of over 30GB of files, it does this same thing and the free space indicator hardly changes. And yes, I've emptied the trash. Sometimes, a restart would increase the free space indicator but nowhere near what it should be. The interesting thing is that when I use Omni Disk Sweeper, it shows that I'm using a smaller amount of disk space than the built in Disk Utility of OSX. For example, Omni Disk would say I'm using 115GB whereas Disk Utility would say I'm using 160GB. What's going on?!