After having MC15 and MC16 installed in parallel, I recently deinstalled MC15,CCCP and QT Lite, so that I can properly test the new Red October features. So far so good, all my mkv videos are playing very well and even most .mov movies (just one test .mov file did not work).
But I have some other problems with screengrabs. I downloaded quite a large number of music videos from YouTube and in many cases I created new thumbnails using the screengrab feature. So in MC15 in AppData there was a folder Data\ScreenGrabs. When I installed MC16 in parallel with MC15 some month ago obviously this folder was not migrated to MC16 and the thumbnails were empty!
I must admit that for some time I downloaded stuff both in MC15 and MC16 as I thought that auto-import would import everything new in MC16. But in MC16 there has never been a folder Data\ScreenGrabs and no screengrabs were displayed except the ones that were never created manually. Even when I copied over the folder from MC15, the screengrabs were not recreated in MC16. I had to recreate all of them manually again.
Now in MC16 I see that the image file tag points to the Data\ScreenGrabs folder. Everything works well now.
But then I also tested library server with the latest version of MC16 and although all music videos play without problem on the client pc, there are no screengrabs images on the client pc (just a dozen out of 200 files). I am not sure how the whole system works, but I think something is missing here!