avconv: merge configuration code for complex and simple filters

Some tests change because -s now inserts the scaler to the end instead
of beginning of the filtergraph.

tests/lavf-regression.sh

@@ -67,7 +67,7 @@ do_lavf mxf "-ar 48000" "-bf 2 -timecode_frame_start 264363"
 fi
 
 if [ -n "$do_mxf_d10" ]; then
-do_lavf mxf_d10 "-ar 48000 -ac 2" "-r 25 -s 720x576 -vf pad=720:608:0:32 -vcodec mpeg2video -g 0 -flags +ildct+low_delay -dc 10 -non_linear_quant 1 -intra_vlc 1 -qscale 1 -ps 1 -qmin 1 -rc_max_vbv_use 1 -rc_min_vbv_use 1 -pix_fmt yuv422p -minrate 30000k -maxrate 30000k -b 30000k -bufsize 1200000 -top 1 -rc_init_occupancy 1200000 -qmax 12 -f mxf_d10"
+do_lavf mxf_d10 "-ar 48000 -ac 2" "-r 25 -vf scale=720:576,pad=720:608:0:32 -vcodec mpeg2video -g 0 -flags +ildct+low_delay -dc 10 -non_linear_quant 1 -intra_vlc 1 -qscale 1 -ps 1 -qmin 1 -rc_max_vbv_use 1 -rc_min_vbv_use 1 -pix_fmt yuv422p -minrate 30000k -maxrate 30000k -b 30000k -bufsize 1200000 -top 1 -rc_init_occupancy 1200000 -qmax 12 -f mxf_d10"
 fi
 
 if [ -n "$do_ts" ] ; then

tests/ref/fate/idroq-video-encode

-5090bb74bad2ea17093c32682b608dc4
+2ac89fa0e5600152667bcbc661f06cfe