+ void add_image_subtitle (std::string id, ContentTimePeriod period);
+ void add_text_subtitle (std::string id, ContentTimePeriod period);
+ std::list<ContentTimePeriod> image_subtitles_during (ContentTimePeriod period, bool starting) const;
+ std::list<ContentTimePeriod> text_subtitles_during (ContentTimePeriod period, bool starting) const;
+ ContentTime find_subtitle_to (std::string id) const;
+ void add_offset (ContentTime offset);
+ void set_colour (RGBA from, RGBA to);
+ std::map<RGBA, RGBA> colours () const;
+
+private: