You may want to configure VLC
to run only one instance at a given time, specially when there are multiple media formats associated to the program.
- Open VLC,click on the Tools menu > Preferences > Interface tab
- Scroll to the "Instance" section
- Check the box next to " Allow only one instance"
Note that enabling this option will also give you access to the " Enqueue files when in one instance mode"
Validate with the "Save" button