For videos, "alt-text" is "title," and should take the form: Videos: <iframe title="Video of Lab Tour" src="https://academiccommons.columbia.edu/doi/10.7916/d8-s5bf-w581/embed" width="640" height="360" frameborder="0" allowfullscreen></iframe>
Do this for all videos in annotations, essays, and edition-webpages