I use Flash CC 2015.
When I generate the video file Flash Media Encoder opened to generate the mp4 file.
The generation ended smoothly.
But when I was watching the movie was muted. Is it a configuration problem? Or used any feature of Flash that should not? I'm waiting for aid.
I encoutered some problem too with flash cc and videos. My mp4 export from media encoder had sound when opening with Quicktime but not in flash. Then i changed the mp4 preset in Media encoder (720p for Android in my case) and the it worked nicely.
Hope it help a bit.