MBAFF: Disable adaptive MBAFF when subme 0 is used

common/common.h

@@ -574,6 +574,7 @@ struct x264_t
         int     i_psy_trellis; /* Psy trellis strength--fixed point value*/
 
         int     b_interlaced;
+        int     b_adaptive_mbaff; /* MBAFF+subme 0 requires non-adaptive MBAFF i.e. all field mbs */
 
         /* Allowed qpel MV range to stay within the picture + emulated edge pixels */
         int     mv_min[2];

encoder/encoder.c

@@ -1035,6 +1035,10 @@ x264_t *x264_encoder_open( x264_param_t *param )
     h->mb.i_mb_width = h->sps->i_mb_width;
     h->mb.i_mb_height = h->sps->i_mb_height;
     h->mb.i_mb_count = h->mb.i_mb_width * h->mb.i_mb_height;
+    /* Adaptive MBAFF and subme 0 are not supported as we require halving motion
+     * vectors during prediction, resulting in hpel mvs.
+     * The chosen solution is to make MBAFF non-adaptive in this case. */
+    h->mb.b_adaptive_mbaff = h->param.b_interlaced && h->param.analyse.i_subpel_refine;
 
     /* Init frames. */
     if( h->param.i_bframe_adaptive == X264_B_ADAPT_TRELLIS && !h->param.rc.b_stat_read )
@@ -2030,10 +2034,13 @@ static int x264_slice_write( x264_t *h )
             x264_fdec_filter_row( h, i_mb_y, 1 );
 
         if( h->param.b_interlaced )
+        {
+            if( h->mb.b_adaptive_mbaff )
             {
                 if( !(i_mb_y&1) )
                     h->mb.b_interlaced = 1;
                 x264_zigzag_init( h->param.cpu, &h->zigzagf, h->mb.b_interlaced );
+            }
             h->mb.field[mb_xy] = h->mb.b_interlaced;
         }