mlt_properties_anim_get_double( properties, "mix", position, length ) :
mlt_transition_get_progress( transition, a_frame );
double inverse = 1.0 - mix;
mlt_properties_anim_get_double( properties, "mix", position, length ) :
mlt_transition_get_progress( transition, a_frame );
double inverse = 1.0 - mix;