I like how sarcastic it is that link to this completely inaccessible post written as PNG image is at HN just next to the link to Bogota's gov page which has a sign language titles :)
There is a link to the transcript, and the link has alt text indicating what it is.
Why bother with subtitles when I have a copy of the screenplay right here?
Wouldn't it be more the opposite? Someone's elsewhere in these comments noting that a screen reader can navigate through the structure of paragraphs much better than blobs of alt text.
Subtitles are blobs of text alternatives (to sound) consumed alongside the other content. As you point out, it's important that they're accurate and well-constructed!