diff --git a/pyffmpeg/__init__.py b/pyffmpeg/__init__.py
index f8cc9fc..bbab5e0 100644
--- a/pyffmpeg/__init__.py
+++ b/pyffmpeg/__init__.py
@@ -151,7 +151,8 @@ def convert(self, input_file, output_file):
         except:
             self.quit()
 
-        if 'Output #0' not in stderr:
+        # This code could be optimized
+        if stderr and 'Output #0' not in stderr:
             lines = stderr.splitlines()
             if len(lines) > 0:
                 self.error = lines[-1]