The codebook generator algorithm involves picking three

different codebook centroids ("high utility", "low
utility" and "closest to the low utility one"). This
change avoid the corner case of choosing two times the
same centroid.

Originally committed as revision 14340 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/elbg.c

@@ -299,8 +299,10 @@ static void do_shiftings(elbg_data *elbg)
             if (elbg->utility_inc[elbg->numCB-1] == 0)
                 return;
 
-            idx[1] = get_high_utility_cell(elbg);
             idx[2] = get_closest_codebook(elbg, idx[0]);
+            do {
+                idx[1] = get_high_utility_cell(elbg);
+            } while (idx[1] == idx[0] || idx[1] == idx[2]);
 
             try_shift_candidate(elbg, idx);
         }