val granulerate_function : Types.mediaType -> string -> 
                    (Types.granulePos -> float option);;

val last_gp_function : Types.mediaType -> string ->
                    string -> string -> Types.granulePos -> Types.granulePos;;

val next_gp_function : Types.mediaType -> string ->
                    string -> string -> Types.granulePos -> Types.granulePos;;