make -i option mandatory

Signed-off-by: Niv Sardi <xaiki@evilgiggle.com>
kill unused ffmpeg opt

Signed-off-by: Niv Sardi <xaiki@evilgiggle.com>
add audio opt

Signed-off-by: Niv Sardi <xaiki@evilgiggle.com>
check non-empty on mlt_do

Signed-off-by: Niv Sardi <xaiki@evilgiggle.com>