How to run two commands simultaneously?

Solution 1:

Start up multiple background tasks. This means that the second one does not need to wait for the first one to finish loading. The & tell the command to run in the background.

From the command-line: In the first one, the number of . (dots) equals the number of instances.

set "/my/vid/path.mp4"   
for i in . . ;do (mplayer "$1" &) ;done   

or

set "/my/vid/path.mp4"; ( 
mplayer "$1" &
mplayer "$1" & )

or

( mplayer "/my/vid/path.mp4" &
  mplayer "/my/vid/path.mp4" & ) 

Or in a script called by play-two "/my/vid/path.mp4"

#!/bin/bash
mplayer "$1" &
mplayer "$1" &

Solution 2:

GNU parallel

In your particular case:

parallel  mplayer ::: file1.avi file2.avi