Are you certain this is by Guillame Dufay? I do not think you have given me the correct music that matches the audio recording in the initial linked page.

Sorry about that, I looked on the DIAMM DuFay Opera Omnia page (which is a work in progress and does not have the Mittit ... ) and saw the Mitchell Trent editions page, mistakenly thinking it was for DuFay as well.

The "Mittit ad virginem" I gave above is from the Trent Codices Tr91, and I agree with MJO that it is a fine work, apparently anonymous.

Upon further search, I found that a setting attributed to DuFay in Tr92, leaves 069v, 070r, and 070v, digitizations at Trentino Cultura. The digitization is not that easy to read, and I have yet to find it transcribed, but it is exactly the work that is on the recording above.