Detect spatial direct MBs partitioned smaller than 16x16 that can be partitioned

as 16x16 (except ones changing interlacing relative to the colocated MB).
20 cycles slower during MV generation
175 cycles faster during MC

Originally committed as revision 21690 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264_direct.c

@@ -319,6 +319,7 @@ single_col:
             fill_rectangle(&h->mv_cache[0][scan8[0]], 4, 4, 8, a, 4);
             fill_rectangle(&h->mv_cache[1][scan8[0]], 4, 4, 8, b, 4);
         }else{
+            int n=0;
             for(i8=0; i8<4; i8++){
                 const int x8 = i8&1;
                 const int y8 = i8>>1;
@@ -344,6 +345,7 @@ single_col:
                                 fill_rectangle(&h->mv_cache[0][scan8[i8*4]], 2, 2, 8, 0, 4);
                             if(ref[1] == 0)
                                 fill_rectangle(&h->mv_cache[1][scan8[i8*4]], 2, 2, 8, 0, 4);
+                            n+=4;
                         }
                     }else{
                         int m=0;
@@ -359,9 +361,12 @@ single_col:
                     }
                     if(!(m&3))
                         h->sub_mb_type[i8]+= MB_TYPE_16x16 - MB_TYPE_8x8;
+                    n+=m;
                     }
                 }
             }
+            if(!is_b8x8 && !(n&15))
+                *mb_type= (*mb_type & ~(MB_TYPE_8x8|MB_TYPE_16x8|MB_TYPE_8x16|MB_TYPE_P1L0|MB_TYPE_P1L1))|MB_TYPE_16x16|MB_TYPE_DIRECT2;
         }
     }else{ /* direct temporal mv pred */
         const int *map_col_to_list0[2] = {h->map_col_to_list0[0], h->map_col_to_list0[1]};