[jitter] jit.record to record a 1-plane matrix?

Hi all. An extremely simple question: 
I am trying to record a normal 4-plane clip into a 1-plane clip file (only luminity information, black and white). 

I use [rgb2luma] which results of course in a 1 plane matrix, but when I try to record it on a file with [jit.record] it becomes a 4-plane video again. I checked the documentation but I didn't see how to do this ... Any suggestion?
Thanks


#P window setfont "Sans Serif" 9.;
#P window linecount 1;
#P message 50 87 88 196617 cancelframedump;
#P button 47 34 17 0;
#P message 47 61 60 196617 framedump;
#P window setfont "Fixedwidth Serif" 10.;
#P message 378 221 43 1441802 getfps;
#P newex 428 179 58 1441802 sel done;
#P newex 270 275 124 1441802 pack write 15. h263;
#P flonum 359 155 39 10 0 0 0 22 0 0 0 221 221 221 222 222 222 0 0 0;
#P newex 378 200 38 1441802 sel 1;
#P newex 320 178 68 1441802 unpack s 0;
#P newex 396 338 38 1441802 print;
#P message 411 275 32 1441802 stop;
#P newex 270 314 136 1441802 jit.qt.record 720 576;
#B color 5;
#P window setfont "Sans Serif" 9.;
#P newex 320 126 127 196617 route read fps framedump;
#P newex 153 139 66 196617 jit.rgb2luma;
#P message 212 65 40 196617 getdim;
#P user jit.fpsgui 153 237 55 196617 0;
#P user jit.pwindow 152 172 79 58 0 1 0 0 1 0;
#P message 117 62 30 196617 read;
#P toggle 153 37 14 0;
#P newex 153 62 57 196617 qmetro 40;
#P newex 153 95 105 196617 jit.qt.movie 720 576;
#P window linecount 2;
#P comment 79 30 60 196617 press to record;
#P connect 20 0 19 0;
#P fasten 20 0 16 0 52 54 40 54 40 269 275 269;
#P fasten 21 0 1 0 55 110 143 110 143 89 158 89;
#P connect 8 0 5 0;
#P fasten 8 0 10 0 158 162 253 162 253 297 275 297;
#P connect 1 0 8 0;
#P fasten 9 2 17 0 403 152 433 152;
#P connect 14 0 18 0;
#P connect 13 1 14 0;
#P connect 9 1 15 0;
#P connect 9 0 13 0;
#P fasten 1 1 9 0 253 113 265 113 265 88 325 88;
#P fasten 17 0 11 0 433 254 416 254;
#P connect 10 1 12 0;
#P fasten 15 0 16 1 364 254 332 254;
#P fasten 11 0 10 0 416 310 275 310;
#P connect 16 0 10 0;
#P connect 5 0 6 0;
#P connect 18 0 1 0;
#P connect 2 0 1 0;
#P fasten 19 0 1 0 52 83 158 83;
#P fasten 7 0 1 0 217 87 158 87;
#P fasten 4 0 1 0 122 83 158 83;
#P connect 3 0 2 0;
#P window clipboard copycount 22;