sanity check

Originally committed as revision 3047 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.c

@@ -956,7 +956,13 @@ int MPV_encode_init(AVCodecContext *avctx)
         av_log(avctx, AV_LOG_ERROR, "b frames not supported by codec\n");
         return -1;
     }
-    
+
+    if((s->flags & (CODEC_FLAG_INTERLACED_DCT|CODEC_FLAG_INTERLACED_ME|CODEC_FLAG_ALT_SCAN)) 
+       && s->codec_id != CODEC_ID_MPEG4 && s->codec_id != CODEC_ID_MPEG2VIDEO){
+        av_log(avctx, AV_LOG_ERROR, "interlacing not supported by codec\n");
+        return -1;
+    }
+        
     if(s->mpeg_quant && s->codec_id != CODEC_ID_MPEG4){ //FIXME mpeg2 uses that too
         av_log(avctx, AV_LOG_ERROR, "mpeg2 style quantization not supporetd by codec\n");
         return -1;