pcDuino3 defaults to output its audio to the audio jack. If we would need to output to HDMI, we can modify the default output of alsa. The method is shown below:

Create a file named .asoundrc under /home/ubuntu, the content is shown below:

 pcm.!default {
 type hw
 card 1 #change to 0 to use HP, 1 HDMI
 }
 
 ctl.!default {
   type hw
   card 1 #change to 0 to use HP, 1 HDMI
 }