如何在jwplayer中启用质量选项

jwplayer("player").setup({
  file: "video.mp4",
  qualityLabels: {
    240: "低清晰度",
    480: "标清",
    720: "高清",
    1080: "超清"
  }
});

jwplayer("player").on("ready", function() {
  var qualityButton = document.createElement("button");
  qualityButton.innerHTML = "切换质量";
  qualityButton.onclick = function() {
    var currentQuality = jwplayer("player").getCurrentQuality();
    if (currentQuality === 240) {
      jwplayer("player").setCurrentQuality(480);
    } else if (currentQuality === 480) {
      jwplayer("player").setCurrentQuality(720);
    } else if (currentQuality === 720) {
      jwplayer("player").setCurrentQuality(1080);
    } else {
      jwplayer("player").setCurrentQuality(240);
    }
  };
  document.getElementById("player").appendChild(qualityButton);
});