diff --git a/README.rst b/README.rst
index 6533c53..6727791 100644
--- a/README.rst
+++ b/README.rst
@@ -53,6 +53,12 @@ is transparently given to the `ffmpeg` binary on your system, without any form
 of validation. So if you know how to use the FFmpeg CLI, you know how to use
 ``ffpb`` !
 
+
+Warning : ``ffpb`` works by parsing the text output from ``ffmpeg``, comparing the number
+of processed frames with the total number of frames in the video. If you mess with 
+``ffmpeg``'s verbosity level (for example by adding ``-v warning`` to your command), ``ffpb`` 
+will not be able to display anything.
+
 Using as a library
 ^^^^^^^^^^^^^^^^^^