FULL PRODUCT VERSION :
java version "9.0.4"
Java(TM) SE Runtime Environment (build 9.0.4+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
macOS High Sierra 10.13.3

A DESCRIPTION OF THE PROBLEM :
In Java 9 and later, when you instantiate MediaPlayer, CPU usage exceeds 100%. It occupies one core of multicore. This problem occurs regardless of the playing state of the media.

This has a fatal impact by exerting a high load on the entire system to the same extent as creating an infinite loop. Therefore, it is practically impossible to use MediaPlayer.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) Rewrite the source code media file location for your test.
2) Launch the test application
3) Press play button

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
It has the same level of CPU usage as running in Java 8.
ACTUAL -
The CPU usage rate continues to exceed 100%.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.ToggleButton;
import javafx.scene.layout.BorderPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.media.MediaPlayer.Status;
import javafx.stage.Stage;

public class MediaPlayerCPUUsageTest extends Application{
private MediaPlayer player;

@Override
public void start(Stage primaryStage) throws Exception {
Media media = new Media("file://your.mp3");
ToggleButton playOrStop = new ToggleButton("PLAY");
playOrStop.selectedProperty().addListener((ob, oldValue, newValue)->{
if(newValue.booleanValue()) {
if(player==null) {
// Lazy load
player = new MediaPlayer(media);
player.setCycleCount(MediaPlayer.INDEFINITE);
player.statusProperty().addListener((ob2, oldValue2, newValue2)->{
playOrStop.setText( newValue2==Status.PLAYING?"STOP":"PLAY");
});
}
player.play();
}else {
player.stop();
}
});

BorderPane root = new BorderPane(playOrStop);
Scene scene = new Scene(root, 200, 200);
primaryStage.setScene(scene);
primaryStage.show();

}

public static void main(String[] args) {
Application.launch(args);
}

}
---------- END SOURCE ----------