Index: slicetype.c
===================================================================
--- slicetype.c	(revision 667)
+++ slicetype.c	(working copy)
@@ -246,6 +246,11 @@
 #undef TRY_BIDIR
 #undef SAVE_MVS
 
+/* Evaluate cost of a candidate frame (b), using p0 as L0
+ * and p1 as L1 references.
+ * 2 references different from b => B frame
+ * 1 references different from b => P frame
+ * 0 reference different from b => I frame */
 int x264_slicetype_frame_cost( x264_t *h, x264_mb_analysis_t *a,
                                x264_frame_t **frames, int p0, int p1, int b,
                                int b_intra_penalty )
@@ -322,17 +327,14 @@
     return i_score;
 }
 
-static int scenecut( x264_t *h, x264_frame_t *frame, int pdist )
+static float scenecut_bias( x264_t *h, x264_frame_t *frame)
 {
-    int icost = frame->i_cost_est[0][0];
-    int pcost = frame->i_cost_est[pdist][0];
     float f_bias;
     int i_gop_size = frame->i_frame - h->frames.i_last_idr;
     float f_thresh_max = h->param.i_scenecut_threshold / 100.0;
     /* magic numbers pulled out of thin air */
     float f_thresh_min = f_thresh_max * h->param.i_keyint_min
                          / ( h->param.i_keyint_max * 4 );
-    int res;
 
     if( h->param.i_keyint_min == h->param.i_keyint_max )
         f_thresh_min= f_thresh_max;
@@ -347,7 +349,20 @@
                    * ( i_gop_size - h->param.i_keyint_min )
                    / ( h->param.i_keyint_max - h->param.i_keyint_min );
     }
+    return f_bias;
+}
 
+
+
+
+static int scenecut( x264_t *h, x264_frame_t *frame, int pdist )
+{
+    int icost = frame->i_cost_est[0][0];
+    int pcost = frame->i_cost_est[pdist][0];
+    float f_bias = scenecut_bias(h, frame);
+    int i_gop_size = frame->i_frame - h->frames.i_last_idr;
+    int res;
+
     res = pcost >= (1.0 - f_bias) * icost;
     if( res )
     {
@@ -369,8 +384,9 @@
     int keyint_limit;
     int j;
     int i_mb_count = (h->sps->i_mb_width - 2) * (h->sps->i_mb_height - 2);
-    int cost1p0, cost2p0, cost1b1, cost2p1;
+    int cost1p0, cost2p0, cost1b0, cost2p1;
     int idr_frame_type;
+    int no_b_frames = 0;
 
     assert( h->frames.b_have_lowres );
 
@@ -389,29 +405,67 @@
 
     if( num_frames == 1 )
     {
-no_b_frames:
+        no_b_frames = 1;
+    }
+    else
+    {
+
+        cost2p0 = x264_slicetype_frame_cost( h, &a, frames, 0, 2, 2, 1 );
+        if( frames[2]->i_intra_mbs[2] > i_mb_count / 2 )
+            no_b_frames = 1;
+
+        if (!no_b_frames )
+        {
+            cost1b0 = x264_slicetype_frame_cost( h, &a, frames, 0, 2, 1, 0 );
+            cost1p0 = x264_slicetype_frame_cost( h, &a, frames, 0, 1, 1, 0 );
+            cost2p1 = x264_slicetype_frame_cost( h, &a, frames, 1, 2, 2, 0 );
+//          fprintf( stderr, "PP: %d + %d <=> BP: %d + %d \n",
+//                  cost1p0, cost2p1, cost1b0, cost2p0 );
+            if( cost1p0 + cost2p1 < cost1b0 + cost2p0 )
+                no_b_frames = 1;
+        }
+    }
+
+    cost1p0 = x264_slicetype_frame_cost( h, &a, frames, 0, 1, 1, 0 );
+    if (no_b_frames)
+    {
         frames[1]->i_type = X264_TYPE_P;
         if( h->param.b_pre_scenecut )
         {
-            x264_slicetype_frame_cost( h, &a, frames, 0, 1, 1, 0 );
-            if( scenecut( h, frames[1], 1 ) )
-                frames[1]->i_type = idr_frame_type;
+            if( scenecut( h, frames[1], 1))
+            {
+                int flash_pic = 0;
+
+                if (num_frames > 1)
+                {
+                    if (!scenecut( h, frames[2], 2))
+                    {
+                        // if 0<--2 is not a scene cut, test if 1 could be a "flash" picture
+                        int cost2p0, cost2p1;
+
+                        cost2p0 = x264_slicetype_frame_cost( h, &a, frames, 0, 2, 2, 1 );
+                        cost2p1 = x264_slicetype_frame_cost( h, &a, frames, 1, 2, 2, 0 );
+
+                        if (cost2p0 < cost2p1) //real evaluation would be: (costIntra1 + cost2p0 < costIntra1 + cost2p1)
+                            flash_pic = 1;
+                    }
+                }
+
+                if (flash_pic)
+                {
+                    no_b_frames = 0;
+                    frames[1]->i_type = X264_TYPE_B;
+                }
+                else
+                {
+                    frames[1]->i_type = idr_frame_type;
+                }
+            }
         }
-        return;
+        if (no_b_frames)
+            return;
     }
 
-    cost2p1 = x264_slicetype_frame_cost( h, &a, frames, 0, 2, 2, 1 );
-    if( frames[2]->i_intra_mbs[2] > i_mb_count / 2 )
-        goto no_b_frames;
-
-    cost1b1 = x264_slicetype_frame_cost( h, &a, frames, 0, 2, 1, 0 );
-    cost1p0 = x264_slicetype_frame_cost( h, &a, frames, 0, 1, 1, 0 );
-    cost2p0 = x264_slicetype_frame_cost( h, &a, frames, 1, 2, 2, 0 );
-//  fprintf( stderr, "PP: %d + %d <=> BP: %d + %d \n",
-//           cost1p0, cost2p0, cost1b1, cost2p1 );
-    if( cost1p0 + cost2p0 < cost1b1 + cost2p1 )
-        goto no_b_frames;
-
 // arbitrary and untuned
 #define INTER_THRESH 300
 #define P_SENS_BIAS (50 - h->param.i_bframe_bias)