Introduce RV3-specific motion vector prediction.

Now B-frames in RV3 look almost correct.

Originally committed as revision 15764 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/rv34.c

@@ -556,6 +556,55 @@ static void rv34_pred_mv_b(RV34DecContext *r, int block_type, int dir)
         fill_rectangle(cur_pic->motion_val[!dir][mv_pos], 2, 2, s->b8_stride, 0, 4);
 }
 
+/**
+ * motion vector prediction - RV3 version
+ */
+static void rv34_pred_mv_rv3(RV34DecContext *r, int block_type, int dir)
+{
+    MpegEncContext *s = &r->s;
+    int mv_pos = s->mb_x * 2 + s->mb_y * 2 * s->b8_stride;
+    int A[2] = {0}, B[2], C[2];
+    int i, j;
+    int mx, my;
+    int avail_index = avail_indexes[0];
+
+    if(r->avail_cache[avail_index - 1]){
+        A[0] = s->current_picture_ptr->motion_val[0][mv_pos-1][0];
+        A[1] = s->current_picture_ptr->motion_val[0][mv_pos-1][1];
+    }
+    if(r->avail_cache[avail_index - 4]){
+        B[0] = s->current_picture_ptr->motion_val[0][mv_pos-s->b8_stride][0];
+        B[1] = s->current_picture_ptr->motion_val[0][mv_pos-s->b8_stride][1];
+    }else{
+        B[0] = A[0];
+        B[1] = A[1];
+    }
+    if(!r->avail_cache[avail_index - 4 + 2]){
+        if(r->avail_cache[avail_index - 4] && (r->avail_cache[avail_index - 1])){
+            C[0] = s->current_picture_ptr->motion_val[0][mv_pos-s->b8_stride-1][0];
+            C[1] = s->current_picture_ptr->motion_val[0][mv_pos-s->b8_stride-1][1];
+        }else{
+            C[0] = A[0];
+            C[1] = A[1];
+        }
+    }else{
+        C[0] = s->current_picture_ptr->motion_val[0][mv_pos-s->b8_stride+2][0];
+        C[1] = s->current_picture_ptr->motion_val[0][mv_pos-s->b8_stride+2][1];
+    }
+    mx = mid_pred(A[0], B[0], C[0]);
+    my = mid_pred(A[1], B[1], C[1]);
+    mx += r->dmv[0][0];
+    my += r->dmv[0][1];
+    for(j = 0; j < 2; j++){
+        for(i = 0; i < 2; i++){
+            s->current_picture_ptr->motion_val[0][mv_pos + i + j*s->b8_stride][0] = mx;
+            s->current_picture_ptr->motion_val[0][mv_pos + i + j*s->b8_stride][1] = my;
+        }
+    }
+    if(block_type == RV34_MB_B_BACKWARD || block_type == RV34_MB_B_FORWARD)
+        fill_rectangle(s->current_picture_ptr->motion_val[!dir][mv_pos], 2, 2, s->b8_stride, 0, 4);
+}
+
 static const int chroma_coeffs[3] = { 0, 3, 5 };
 
 /**
@@ -741,7 +790,10 @@ static int rv34_decode_mv(RV34DecContext *r, int block_type)
     case RV34_MB_B_BACKWARD:
         r->dmv[1][0] = r->dmv[0][0];
         r->dmv[1][1] = r->dmv[0][1];
-        rv34_pred_mv_b  (r, block_type, block_type == RV34_MB_B_BACKWARD);
+        if(r->rv30)
+            rv34_pred_mv_rv3(r, block_type, block_type == RV34_MB_B_BACKWARD);
+        else
+            rv34_pred_mv_b  (r, block_type, block_type == RV34_MB_B_BACKWARD);
         rv34_mc_1mv     (r, block_type, 0, 0, 0, 2, 2, block_type == RV34_MB_B_BACKWARD);
         break;
     case RV34_MB_P_16x8: