Zoom & Pan filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>
use internal frame counting instead of outlink one

Signed-off-by: Paul B Mahol <onemda@gmail.com>
silence boring warning

Signed-off-by: Paul B Mahol <onemda@gmail.com>
do not reconfigure filtergraph on parameters change

Signed-off-by: Paul B Mahol <onemda@gmail.com>
support changing frame properties on the fly

Signed-off-by: Paul B Mahol <onemda@gmail.com>