I still have the issue with Ubuntu 14.04 as I had on Mint 17.3: My laptop is connected to the TV via HDMI. Everything works fine. If I shut down the computer and plug off the HDMI no sound is coming from the internal speakers for some(?) video files. Sometimes youtube videos are affected too. Other sounds (system notifications, alerts and test sounds) work fine.
Clicking in the sound settings on internal speaker does not help. A reboot does not work either.
The only way to get the sound for the video file is to go back to the TV, plug in the HDMI and then select internal speaker output. Then I can unplug HDMI again.
But what if I don't have a HDMI cable available?
Thanks for your help. (LAPTOP is TUXEDO with Ubuntu 16.04)