/** Called by subclasses when an image subtitle is ready.
* Image may be 0 to say that there is no current subtitle.
+ * @param rect Area expressed as a fraction of the video frame that this subtitle
+ * is for (e.g. a width of 0.5 means the width of the subtitle is half the width
+ * of the video frame)
*/
void
SubtitleDecoder::image_subtitle (ContentTimePeriod period, shared_ptr<Image> image, dcpomatic::Rect<double> rect)