I used to back up my DVDs with RipIt, but found that it couldn’t handle some DVDs that MDRP could, so I switched. Whereas RipIt extracts the DVD contents to a .dvdmedia folder (playable by Apple’s DVD player application), MDRP has an option to rip the DVD to a single .iso file, which is playable in VLC and XBMC.
I then wanted to convert my .dvdmedia folders into .iso files. In theory a .iso is just a file container, so my first attempt was to use Disk Utility to make a CD .img of the folder and then rename it to .iso. This kind of worked, in that VLC did begin to play something when pointed at the .iso, but there were weird issues – no DVD menu, no audio, or the wrong language.
It turns out that the structure of the .iso is important, and just dumping the DVD files into it isn’t good enough. I found a forum post out there (which unfortunately I can’t find again) which pointed me at a command line tool called mkisofs, which I was familiar with from work when mastering multimedia CDs for replication.
Unfortunately mkisofs isn’t available by default, but you can get it from the Homebrew package manager.
Once installed, the command you need is
mkisofs -dvd-video -o output.iso input.dvdmedia
It didn’t work for all my .dvdmedia rips, but did for most.