anchor.diff:    {bitstream_filters,      output, "-bsf",                   [{{?MODULE, is_list_and_list}, to_dotargs}, {{erlang, is_list}, to_arg}]},
     {timecode,               output, "-timecode",              [{{erlang, is_list}, to_arg}]},
     {strict,                 output, "-strict",                [{{erlang, is_list}, to_arg}]},
  +  {metadata,               output, "-metadata",              [{{?MODULE, is_list_and_list}, to_kvarg}]},
   
     {x264_profile,           output, "-profile",               [{{?MODULE, is_list_and_list}, to_dotargs}]},
     {x264_level,             output, "-level",                 [{{erlang, is_float}, to_arg}]},
  
positive.code:   ":" ++ X ++ " " ++ float_to_list(Y);
  to_dotargs([X, true]) when is_list(X) ->
    ":" ++ X.
  
  
negative.code:     is_integer_and_float/1,
      to_nothing/1,
      to_arg/1,
      to_dotargs/1,
      to_kvarg/1
  ]).
  
  -define(OPTIONS, [
  