diff --git a/libmpcodecs/vd_ffmpeg.c b/libmpcodecs/vd_ffmpeg.c
 index 7c68a20..135e6b1 100644
 --- a/libmpcodecs/vd_ffmpeg.c
 +++ b/libmpcodecs/vd_ffmpeg.c
 @@ -280,7 +280,7 @@ static int init(sh_video_t *sh){
          return 0;
      }
  
 -    if(vd_use_slices && (lavc_codec->capabilities&CODEC_CAP_DRAW_HORIZ_BAND) && !do_vis_debug)
 +    if(vd_use_slices && (lavc_codec->capabilities&CODEC_CAP_DRAW_HORIZ_BAND) && !do_vis_debug && lavc_param_threads <= 1)
          ctx->do_slices=1;
  
      if(lavc_codec->capabilities&CODEC_CAP_DR1 && !do_vis_debug && lavc_codec->id != CODEC_ID_H264 && lavc_codec->id != CODEC_ID_INTERPLAY_VIDEO && lavc_codec->id != CODEC_ID_ROQ && lavc_codec->id != CODEC_ID_VP8 && lavc_codec->id != CODEC_ID_LAGARITH)