rasterize
abstract fun rasterize(cues: List<SubtitleCue>, viewportWidth: Int, viewportHeight: Int, fontScale: Float, position: Float = 1.0f): List<OverlayImage>
Parameters
position
where the implicit bottom stack anchors, as a fraction of the viewport height: 1.0 is the ordinary bottom edge, 0.5 mid-screen, mpv's sub-pos over 100. Explicitly positioned cues are the author's word and do not move with it.