Since Version 5, there is an easy way to redirect the output: Simply put a file named “alsa.txt” on the /boot drive, whith only one number in it. On Raspi, 0 should be HDMI, 1 should be Onboard Analog, 2 would be an external card. If there is no file present, it defaults to 0. When logged in, see below how to find your card number via “aplay -l”. You could also use trial&error by using numbers counting up from 1 until you find your correct output.
Find out your sound output number
Check out the HowTo Hack to get access to the command line.
Now let’s check on the current configuration of the system
This option of aplay (which is an audio player) gives you a list of the devices present. Please note that these numbers will be different, depending on the configuration of your Pi, if a display is connected with HDMI Audio, etc.
Open the mixer with alsamixer, make your changes and exit with the Escape Key.
If you want to make your changes permanent, store your configuration with the following command:
sudo alsactl store
Note: Some Soundcards do not allow for Volume Control with the mixer. The volume can only changed through alsamixer if you have changed the audio output device in the mp4museum.py script.