h264: increase dist_scale_factor for up to 32 references

Compute dist_scale_factor_field only for MBAFF since that is the only
case in which it is used.

libavcodec/h264.h

@@ -364,7 +364,7 @@ typedef struct H264Context {
     int direct_spatial_mv_pred;
     int col_parity;
     int col_fieldoff;
-    int dist_scale_factor[16];
+    int dist_scale_factor[32];
     int dist_scale_factor_field[2][32];
     int map_col_to_list0[2][16 + 32];
     int map_col_to_list0_field[2][2][16 + 32];

libavcodec/h264_direct.c

@@ -54,14 +54,17 @@ void ff_h264_direct_dist_scale_factor(H264Context * const h){
     const int poc = h->s.current_picture_ptr->field_poc[ s->picture_structure == PICT_BOTTOM_FIELD ];
     const int poc1 = h->ref_list[1][0].poc;
     int i, field;
-    for(field=0; field<2; field++){
-        const int poc  = h->s.current_picture_ptr->field_poc[field];
-        const int poc1 = h->ref_list[1][0].field_poc[field];
-        for(i=0; i < 2*h->ref_count[0]; i++)
-            h->dist_scale_factor_field[field][i^field] = get_scale_factor(h, poc, poc1, i+16);
-    }
 
-    for(i=0; i<h->ref_count[0]; i++){
+    if (FRAME_MBAFF)
+        for (field = 0; field < 2; field++){
+            const int poc  = h->s.current_picture_ptr->field_poc[field];
+            const int poc1 = h->ref_list[1][0].field_poc[field];
+            for (i = 0; i < 2 * h->ref_count[0]; i++)
+                h->dist_scale_factor_field[field][i^field] =
+                    get_scale_factor(h, poc, poc1, i+16);
+        }
+
+    for (i = 0; i < h->ref_count[0]; i++){
         h->dist_scale_factor[i] = get_scale_factor(h, poc, poc1, i);
     }
 }