Whenever I try to export the movie, iMovie crashes.
I called Apple official support. He said you shold switch from the old version iMovie to the new one. Because it sometimes doesn't work on latest OS(Sierra) so he recommend to use latest iMovie when you use latest OS.
Sierra 10.12.1(not changed)
If you have same trouble, you can reffer to this.
I felt Apple official support is very good service. Firstly he said "I'm sorry to trouble you. Don't worry. I'll do my best to troubleshoot." When this trouble was solved, he said "I'm sorry to waste a lot of your time." But the time I talked with him was about 10 min. I thougt that wasn't so long time. He was talking very respectivelly to me over the phone. He impressed me favorablly.