It is astounding that this problem still persists since 2013. I haven't been able to make a movie with iMovie 10 since it came out. I tried importing from my Sony DCR -TRV460 about 4 times yesterday and was never able to accomplish the task. I was trying to import a 1 hour video of a youth event; import was started and I returned later only to discover that it only imported a couple of short clips. Finally discovered that it had run out of memory with no warning or reminders after only 15 minutes. After clearing the memory and relocating the library to an external drive I tried twice more and still it failed; there was more than 3 hours of space available. Each time, only a few clips were imported; less than 5 minutes out of the whole hour. Finally I searched the web and found this thread and was reminded to revert back to iMovie version 9 and earlier with which I had made dozens of movies over the years. Version 9 showed me right up front how much memory was available to store the video.
iMovie 10 just wasted about 3 hours of my time; it is a horrible product. It seems Apple tried to make it simpler to use but totally failed by changing everything so it was very difficult to figure out how to use.
