iMovie 09/OS X El Capitan: export project but no sound

I was having the same problem with iMovie 09' but on high sierra. I found a very specific set of steps that seemed to resolve the problem:

-make a small edit so that iMovie has to re-render the movie (i slightly adjusted the timing of a sound track)

-Share > export using QuickTime

video settings: H.264

audio settings: AAC

Save

-Wait for it to export

Then... Share > Export Movie...

For some reason this got it to export with sound. Very strange, but it worked.

Not sure if this solves your problem, but I had the same problem with I exported a video file using iMovie '09 after upgrading to El Cap.

In my case, I didn't add any background music, but the file that exported (using the "Share-->Export Movie" and then trying the "Share-->Export using QuickTime) had only video, no sound.

I ended up trying it again with a smaller file to test different settings. I used the "Export using QuickTime" and under the file type I chose "Movie to QuickTime Movie" and then clicked 'Options' and went through all of the video and audio options, including 'preview audio'.

After going through all of the Options, I then clicked 'save' and the final export had the sound and video.

Since doing this, I have been able to export as both QuickTime files and MPEG-4 files and the sound comes with the video.

Here are screenshots (in this example, I'm exporting under "Export using QuickTime" and chose "Movie to MPEG-4"):

When I looked at the original files that had only video and no audio, only the video codec was exported, not the video and audio codecs.

Not sure why going through the exercise of looking at all of the "Options" tabs worked to export both the video and audio codecs but it did!