void video (boost::weak_ptr<Piece>, ContentVideo);
void audio (boost::weak_ptr<Piece>, AudioStreamPtr, ContentAudio);
void image_subtitle_start (boost::weak_ptr<Piece>, ContentImageSubtitle);
void text_subtitle_start (boost::weak_ptr<Piece>, ContentTextSubtitle);
void subtitle_stop (boost::weak_ptr<Piece>, ContentTime);
void video (boost::weak_ptr<Piece>, ContentVideo);
void audio (boost::weak_ptr<Piece>, AudioStreamPtr, ContentAudio);
void image_subtitle_start (boost::weak_ptr<Piece>, ContentImageSubtitle);
void text_subtitle_start (boost::weak_ptr<Piece>, ContentTextSubtitle);
void subtitle_stop (boost::weak_ptr<Piece>, ContentTime);