tac - concatenate or print in reverse (last line first).

tac > f1

1 2 Press CTRL+D to stop

tac f1

1 2

tac vid.avi > vid2.avi ; mv vid2.avi vid.avi

It wont play.

tac vid.avi > vid2.avi ; mv vid2.avi vid.avi

Back to playable.

NOTE: This is like a mini encryption for binary files.