My mac tower and Premere worked fine until I upgraded to High Sierra. Prior to that, things were close to perfect. Now I can't open mts files in OS. It's the new Quicktime that they built into High Sierra.It's now a separate program anymore. 2017 Premiere doesn't work either. Oddly, I discovered that my old Prelude 2015 works fine. Also a note, both Apple and Adobe act like there are no problems... both relate as if I'm a beginner who has some toy cameras and have no idea what I'm doing after a career of network production for over 40 years. I even talked to a friend at DV Magazine today who tested my mts problem and she got the same result. Apple is ignoring this elephant in the room. Hundreds of people have posted about it.