         slider.setProgress(volume, animated: true)
         
         do { try setSystem(volume: value) }
-        catch { NSLog("unable to change system volume level.") }
+        catch { print("unable to change system volume level.") }
        
         UIView.animateKeyframes(withDuration: animated ? 2 : 0, delay: 0, options: .beginFromCurrentState, animations: { () -> Void in
             UIView.addKeyframe(withRelativeStartTime: 0, relativeDuration: 0.1, animations: {

    
    @objc private func orientationDidChange(_ notification: Notification) {
        // TODO: [wip] support landscape mode.
        // NSLog("orientation changed.")
        /**
        let currentOrientation = UIDevice.current.orientation
        switch currentOrientation {

    
    private func setupSession(_ options: [VolumizerAppearanceOption]) {
        do { try session.setCategory(AVAudioSessionCategoryPlayback, with: .mixWithOthers) }
        catch { print("Unable to set audio session category.") }
        
        do { try session.setActive(true) }
        catch  { print("Unable to initialize AVAudioSession.") }
        
        volumeView.setVolumeThumbImage(UIImage(), for: UIControlState())
        volumeView.isUserInteractionEnabled = false
