I’d love to echo support for this request. Especially if the title can be simply added to the iFrame with no filters or other actions needing to be taken by a developer. Because this information is most helpful and only visible to assistive technologies, it can just be automatically applied. This SO article may be of some help, as it seems to be easy to retrieve the title of a given video once the URL for it is known, at least for YouTube.
PhP code for getting Title of YouTube video:
https://stackoverflow.com/questions/1216029/get-title-from-youtube-videos
And, here’s a gist, an old one though, I came across that does it for both Vimeo and YouTube:
https://gist.github.com/djekl/5832149
Thank you so much!