+ void add_image_subtitle (std::string id, ContentTimePeriod period);
+ void add_text_subtitle (std::string id, ContentTimePeriod period);
+ void set_subtitle_to (std::string id, ContentTime to);
+ ContentTime find_subtitle_to (std::string id) const;
+ bool unknown_to (std::string id) const;
+ void add_offset (ContentTime offset);
+ void set_colour (RGBA from, RGBA to);
+ std::map<RGBA, RGBA> colours () const;
+
+ bool has_text () const;
+ bool has_image () const;