kdu_compressed_video_source::get_frame_instant

If the video source provides no timing information, this function may return 0. Otherwise, it should return the starting time of the frame to which the currently open image belongs, measured in the time scale (ticks per second) identified by the get_timescale function. If no image is currently open, the function returns the starting time of the next frame which will be opened by open_image, or the duration of the video track if no new frames are available for opening.

Note that the return value should be unaffected by the field mode established by set_field_mode. That is, the function returns frame starting times, not field starting times, when the video is interlaced.