Screen Mirroring Captions Not Working

Hi so i don’t usually ask for anything anywhere but i really want to know why this happens, so when i screen mirror (with a dock connector) a video from safari the captions don’t pop up even tho they come up just fine when i watch the video on my phone an example of this is any video on hianime.to the audio and video come up fine but there’s no captions does anyone know if theres any sort of fix.