This can also happen due to fractional scaling, ( from experience) 
If you run, may help.
sudo apt-get install ubuntu-restricted-extras
ubuntu-restricted-extras is a meta-package that installs:
- Support for MP3 and unencrypted DVD playback
- Microsoft TrueType core fonts
- Flash plugin
- codecs for common audio and video files
Like if you install VLC, you don't have to use VLC, but the Video Player you use, may access a codec from VLC to help.
I also try not to install things i don't need.