Thanks!! You are right. The API changed completely. I now changed the code as follows, and it works.:

use SDL;
use SDL::Mixer;
use SDL::Mixer::Music;

printf("Error initializing SDL_mixer: %s\n", SDL::get_error()) unless 
+SDL::Mixer::open_audio(22050, AUDIO_S16, 2, 1024) == 0;
 
playMusicFile("test.wav");
 
sub playMusicFile
{
    my $music_file = $_[0];        
 
    my $music = SDL::Mixer::Music::load_MUS( $music_file );
    
    SDL::Mixer::Music::volume_music( 40 );
    my $play_music = SDL::Mixer::Music::play_music( $music, 1 );
    print $play_music;

    SDL::delay(10000); # fix delay, better would be a solution to wait
+ until song is finished, I have to find out this later
}
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