Rewrite blank_background

New blank_background version permit to introduce the 'Mute Video'

https://github.com/fcarlier/omxplayer/commit/d89ea34e937e9e0c94fcba3b2e2d5927004ca4de
https://github.com/fcarlier/omxplayer/commit/667f8d7d7c69607f06ca672c8c000dd474435204