Crops the subtitle band (band_top to band_bottom of the frame height) and sample...
https://ton.halowerk.com/v1/burned-subtitle-extractOverview
Crops the subtitle band (band_top to band_bottom of the frame height) and samples it at sample_fps. A text mask keeps bright pixels that have a dark neighbour within 2 px (outline or shadow; the reverse for dark text). A cue is a run of samples with a mask present whose consecutive masks overlap (IoU at least 0.5); runs shorter than min_cue_s are dropped.