To answer myself:
I cleaned the array using:
const mplayerArgumentsArrayFilter = mplayerArgumentsArray.filter(discardEmptyArgument);
function discardEmptyArgument(value, index, array) {
return value != '';
}
Then spawned using that array:
// Spawn a new mplayer process
const env = { ...process.env, DISPLAY: ':0' };
const mplayerProcess = spawn(`mplayer`, mplayerArgumentsArrayFilter, {env: env});
Now it is working correct.