What exactly is an umlaut?

Sure, an umlaut is those two dots over a letter. But what exactly is it? What does it mean, and what started it? My old video about the umlaut: https://www.youtube.com/watch?v=DZaDijq3M2U Chapters: 00:00 When an umlaut isn't an umlaut 01:46 The vowel chart 02:58 Writing the sounds 04:02 Umlautable vowels 05:08 Performing the umlaut 05:35 How it all started Music: "Style Funk" and "Hot Swing" by Kevin MacLeod https://incompetech.com/ Creative Commons Attribution licence --------- Support me on Patreon for access to bonus content and more: http://patreon.com/rewboss Send letters and postcards to: Rewboss Postfach 10 06 29 63704 Aschaffenburg Germany Please don't send parcels or packages, or anything that has to be signed for. --------- My website: http://www.rewboss.com/ My blog: http://rewboss.blogspot.com/ My Twitter feed: https://www.twitter.com/rewboss My Facebook profile: http://facebook.com/rewboss