How to open files via Terminal
To open any file from the command line with the default application, just type open followed by the filename/path.

Example:

open ~/Desktop/filename.mp4


Edit: as per Johnny Drama's comment below, if you want to be able to open files in a certain application, put -a followed by the application's name in quotes between open and the file.

Example:

open -a "QuickTime Player" ~/Desktop/filename.mp4


If you need further information about the open command, type man open.