If you have a <video> element, you can control what frame is displayed before the video is played, by inserting a <poster> element into it. If the page author d

If you have a <video> element, you can control what frame is displayed before the video is played, by inserting a <poster> element into it. If the page author doesn't explicitly specify a poster frame, the browser is free to choose a frame to display. The person who filed the bug is (effectively) saying "if the page author specifies a poster frame, it should be possible to add alt text. If the page author uses the default poster frame, it should be impossible to add alt text." I believe the question Hixie was getting at was "why would you (a blind user) care about an explicitly-set poster frame but not a default poster frame?" which, I think, is reasonable.