Improve stream format error (#950)

Author: mat-hek

CHANGELOG.md

@@ -1,5 +1,8 @@
 # Changelog
 
+## Master
+* Improve stream format error [#950](https://github.com/membraneframework/membrane_core/pull/950)
+
 ## 1.2.0
  * Add `:max_instances` option for dynamic pads. [#876](https://github.com/membraneframework/membrane_core/pull/876)
  * Implement `Membrane.Connector`. [#904](https://github.com/membraneframework/membrane_core/pull/904)

lib/membrane/core/element/stream_format_controller.ex

@@ -118,8 +118,10 @@ defmodule Membrane.Core.Element.StreamFormatController do
           end
 
         raise Membrane.StreamFormatError, """
-        Stream format: #{inspect(stream_format)} is not matching accepted format pattern #{pretty_accepted_format} in def_#{direction}_pad
-        for pad #{inspect(pad_name)} in #{inspect(module)}
+        Stream format: #{inspect(stream_format)} is not matching accepted format pattern \
+        #{pretty_accepted_format} in def_#{direction}_pad for pad #{inspect(pad_name)} \
+        in #{inspect(module)}. Beware that stream format is forwarded by the default implemetation \
+        of handle_stream_format in filters.
         """
       end
     end