Export hangs and is stuck at 0%

I have created a video with a large number of clips. The video is only a little over 20 minutes long, but each clip is typically less than 10 seconds. It plays fine in the editor, but when I try to export it, it is just stuck at 0%. It stays like this for hours. However, VirbExport.exe is running with about 17% CPU, so I'm hoping it will get going eventually.