dnxhd codec is intra only

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@15672 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/utils.c

@@ -746,6 +746,7 @@ static int is_intra_only(AVCodecContext *enc){
         case CODEC_ID_ASV1:
         case CODEC_ID_ASV2:
         case CODEC_ID_VCR1:
+        case CODEC_ID_DNXHD:
             return 1;
         default: break;
         }