Can I remap the Caps Lock key to play audio?

In Ubuntu 16.04 after spending hours googling & fiddling with dconf-editor and xbindkeys I found an extremely easy solution:

• Very quick setup in 2 minutes
• Only xdotool needs to be installed
• No scripts necessary
• Caps lock is still recognized but doesn’t toggle letter case
• Works with standard Ubuntu Keyboard Custom Shortcut Settings

If you need Gnome XF86AudioPlay support you need xdotool (not needed for VLC as OP stipulates):

sudo apt install xdotool

Now here’s the tricky part. Every time you press the Caps LocK key to toggle the music between Play and Pause, capital letters also toggle off and on.

Use this method to turn off Caps Lock toggling while still keeping key active:

setxkbmap -option caps:none

Music players that adhere to Gnome

Then in Ubuntu 16.04 go into Settings » Keyboard » Shortcuts » Custom Shortcuts:

• Set the name to Audio Play
• Set the command to xdotool key XF86AudioPlay
• Then click the Apply button

After adding the new option the assigned shortcut key will read Disabled. Click on Disabled and when prompted for key to assign press the Caps LocK key.

Music players like VLC

Follow the steps for Gnome in the previous section but for the command use this instead:

qdbus org.mpris.MediaPlayer2.vlc /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.PlayPause

VLC won’t recognize media keys: How to make the keyboard media keys to work with VLC globally?y even when built into the keyboard. Therefor the custom keyboard shortcut to XF86AudioPlay is useless with xdotool.

Setting custom keyboard shortcuts from command line

This Q&A discusses how to set custom keyboard shortcuts from the command line: How to set custom keyboard shortcuts from terminal?

Deactivating caps lock permanently

Next step is to make this setxkbmap -option caps:none persistent across reboots. Googling results in this answer by Terdon: Save setxkbdmap settings:

An easy way would be to add the command to your $HOME/.profile file (you can create it if it doesn’t exist):

setxkbmap -option caps:none

That should make it run every time you log in.

Note that you should use $HOME/.profile rather than $HOME/.bash_profile, $HOME/.bashrc or some other similar file. This is because this setting should be read by your login manager.