Provide top_field_first logic for h264

patch by: Reinhard Nissl rnissl a gmx d de

Originally committed as revision 10989 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -7767,6 +7767,8 @@ static int decode_frame(AVCodecContext *avctx,
 
         } else {
             cur->interlaced_frame = FIELD_OR_MBAFF_PICTURE;
+            /* Derive top_field_first from field pocs. */
+            cur->top_field_first = cur->field_poc[0] < cur->field_poc[1];
 
         //FIXME do something with unavailable reference frames