How to associate MIME type with a handler in OS X?

The easiest would be to download and install RCDefaultApp. Go to System Preferences » Default Apps, then the MIME Types tab.

Enter your new MIME type in the text box below, press the + button, and select your handler.

Via command line, you need to edit the ~/Library/Preferences/com.apple.LaunchServices.plist preference list. In its array of LSHandlers, you need to insert a Dictionary containing your new MIME type as:

• LSHandlerContentTag – the MIME type
• LSHandlerContentTagClass, which is public.mime-type
• LSHandlerRoleAll, which specifies the Bundle ID of the application that handles it, e.g. org.videolan.vlc. You find out the bundle ID by inspecting the .app folder and the Info.plist preference list therein.

To view mime-type of a file in terminal:

file --mime-type -b file-name