Teodoro Jesús Boggio Mireles:
Happy feast of St. Augustine!

I remember Canon Hesse mentioned the beautiful sequence of St. Augustine, and I found it a few years ago. 

https://youtu.be/Rv0xGQGOrb0?si=O0nZIDFxAHZzQO9A

It is a little cut off the beginning there. It is sung at an indult chapel.


https://www.youtube.com/live/t4rOzHifETM?si=nYIBB2xPZoEboBY0

It starts a little after 29:50 in this video.

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GregoBase - De profundis tenebrarum!
https://gregobase.selapa.net/chant.php?id=7567

The Rad Trad: Sequence and Preface for St. Augustine
http://theradtrad.blogspot.com/2013/08/sequence-and-preface-for-st-augustine.html

It sounds like the Lauda Sion since it is medieval.

Saint Augustine (died A.D. 430): "No man can find salvation except in the Catholic Church. Outside the Catholic Church one can have everything except salvation. One can have honor, one can have the sacraments, one can sing alleluia, one can answer amen, one can have faith in the name of the Father and of the Son and of the Holy Ghost, and preach it too, but never can one find salvation except in the Catholic Church." (Sermo ad Caesariensis Ecclesia plebem)