But his 18-minute video is still very much worth watching.
When I say “watching,” I mean more than just listening to the accents. Roper takes you though more than six centuries of spoken English—all from the London area—in 60-year intervals. So we get two generations in each jump, enough to notice changes. It’s Roper’s voice that you will hear, so you just have to trust the accuracy of his renditions (more on that below). But do look carefully at the screen the whole time, as you will see not only subtitles but also ever-changing still images of how the vowels have changed as we go through history. It will, of course, help if you can read IPA symbols (as used in the charts above and below, for example), and if you understand the tongue positions of various vowel sounds. Conventionally we use a side view of the inside of the mouth, with the lips at the left, like this chart, which shows standard American vowels:
Let me stress that we’re talking about vowel sounds, not their representation as letters.
Although occasionally Roper clearly slips into his natural modern pronunciation, he certainly sounds accurate to me most of the time—but what do I know? This area of linguistics has never been my speciality. Read the YouTube comments to get various claims of accuracy and inaccuracy from those who might know more than I do. Or not. In any case, it’s a fascinating journey though one slice of English pronunciation from late Middle English through Early Modern English to the present day. Invest 18 minutes of your life (get it? 18? life?), and you’ll learn something.