How to extract the thumbnail images from webvtt file in AVplayer

Question

WEBVTT

00:00.000 --> 00:05.000 assets/bbb-sprite.jpg#xywh=0,0,128,72

00:05.000 --> 00:10.000 assets/bbb-sprite.jpg#xywh=128,0,128,72

00:10.000 --&