warn on interlaced streams

Originally committed as revision 5337 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -7283,6 +7283,8 @@ static inline int decode_seq_parameter_set(H264Context *h){
         return -1;
 
     sps->frame_mbs_only_flag= get_bits1(&s->gb);
+    if(!sps->frame_mbs_only_flag)
+        av_log(h->s.avctx, AV_LOG_ERROR, "interlacing is not supported, picture will probably be garbage\n");
     if(!sps->frame_mbs_only_flag)
         sps->mb_aff= get_bits1(&s->gb);
     else