SUMMARY
When you open an audio player and play something it plays fine. But when you play the same using cron it doesn't work. Video attached.

STEPS TO REPRODUCE USING CLEMENTINE (is the same with VLC or Audacious)
1. Open cron and put this line by entering crontab -e
2. 06 13 * * 1-5 DISPLAY=:0 /usr/bin/clementine /home/soul/Desktop/Playlist/mornplaylist.m3u >/dev/null 2>&1

3. Please change the time as per your time of testing/reproducing.
4. Please change the path of the playlist to your own playlist. In my case the playlist is /home/soul/Desktop/Playlist/mornplaylist.m3u
5. When the time comes and cron executes you get the error "Failed to connect: Connection refused"

OBSERVED RESULT
You get an error something to this effect "Failed to connect: Connection refused"
If you look into the settings of the player (in my case clementine, but it can be any other player of your choice), and look for the audio device. It will not show the default audio device.

EXPECTED RESULT
You should be hearing the song which was played.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
https://drive.google.com/open?id=1nc0dzjoY4Pes1B0rHO-hWEJBsl5sNhXP