/** @param starting true if we want only subtitles that start during the period, otherwise
* we want subtitles that overlap the period.
*/
virtual std::list<ContentTimePeriod> image_subtitles_during (ContentTimePeriod period, bool starting) const = 0;
virtual std::list<ContentTimePeriod> text_subtitles_during (ContentTimePeriod period, bool starting) const = 0;
/** @param starting true if we want only subtitles that start during the period, otherwise
* we want subtitles that overlap the period.
*/
virtual std::list<ContentTimePeriod> image_subtitles_during (ContentTimePeriod period, bool starting) const = 0;
virtual std::list<ContentTimePeriod> text_subtitles_during (ContentTimePeriod period, bool starting) const = 0;