mlt_multitrack_connect( multitrack, mlt_playlist_producer( playlist ), track );
mlt_producer prod = mlt_tractor_producer( tractor );
+ mlt_producer_optimise( prod );
mlt_properties props = mlt_tractor_properties( tractor );
mlt_properties_set_data( props, "group", group, 0, ( mlt_destructor )mlt_properties_close, NULL );
mlt_properties_set_position( props, "length", mlt_producer_get_out( mlt_multitrack_producer( multitrack ) ) + 1 );