T 指定された型にキャストした Playable を返します。キャストに失敗したら、InvalidCastException 例外をスローします。
互換性のある参照型、または、null が可能な型の間である種の型の変換を行うために CastTo メソッドを使用できます。
Some Playables are implemented as internal C++ objects but are exposed as C# structs. This is to allow the possibility of creating Playable graphs without allocating GC memory in your C# scripts. One down side of using structs as opposed to classes, is that struct in C# do not support inheritance. The CastTo method allows you to convert a C# Playable into one of it's "derived C++ class".