While playing back some films ffplay is seen more balanced CPU occupancy then gstreamer.

Sample film: http://dev.lemote.com/files/upload/software/temp/tears_of_steel_720p.mkv

Following change solves this:
diff --git a/ext/libav/gstavviddec.c b/ext/libav/gstavviddec.c
index 0e909a4..f96c21b 100644
--- a/ext/libav/gstavviddec.c
+++ b/ext/libav/gstavviddec.c
@@ -434,7 +434,7 @@ gst_ffmpegviddec_set_format (GstVideoDecoder * decoder,
   } else
     ffmpegdec->context->thread_count = ffmpegdec->max_threads;

-  ffmpegdec->context->thread_type = FF_THREAD_SLICE;
+  ffmpegdec->context->thread_type = FF_THREAD_SLICE | FF_THREAD_FRAME;

   /* open codec - we don't select an output pix_fmt yet,
    * simply because we don't know! We only get it