Hello ATR
A) yes correct - "going with the AVCHD.mts and then converting that to a .mov file in QuickTime before trying to import that .mov file in Premiere Elements 11 Mac."
B) Please can you tell me how I can look up what is the video compression of these trimmed files. Frame rate is 50.000 fps - is that what you are asking? (sorry, I am using German versions of both Quick Time and Premiere Elements).
C) I just tried that, saved the file without trimming as mov with Quick Time, then import to PE11 - same result. I can add it to the timeline but it's slowing down the system to an unusable speed. (As I have explained to Steve, I don't think it can be a hardware problem although I know MacBook Air is not designed for video editing, but with the same size footage out of my 3 Sony cameras it can handle the same type of files just fine).
Andrew- I guess our original question is answered, we can't actually delete parts of the original file in Premiere Elements.... Thanks ATR for that clarification, even if it is bad news at the moment ;-)