a.js

navigator.requestMediaKeySystemAccess("com.microsoft.playready", [
  {
    "initDataTypes":["cenc"],
    "videoCapabilities": [
      { "contentType": "video/mp4;codecs=\"avc1.4d401e\"" },
      { "contentType":"video/mp4;codecs=\"avc1.42e01e\"" },
      { "contentType":"video/webm;codecs=\"vp8\"" }
    ],
    "audioCapabilities": [
      { "contentType":"audio/mp4;codecs=\"mp4a.40.2\"" },
      { "contentType":"audio/webm;codecs=opus" }
    ],
    "distinctiveIdentifier":"optional",
    "persistentState":"optional",
    "sessionTypes":["temporary"]
  },
]).then(
  () => { console.log("com.microsoft.playready: it works"); },
  () => { console.log("com.microsoft.playready: it failed"); }
);
navigator.requestMediaKeySystemAccess("com.microsoft.playready.software", [
  {
    "initDataTypes":["cenc"],
    "videoCapabilities": [
      { "contentType": "video/mp4;codecs=\"avc1.4d401e\"" },
      { "contentType":"video/mp4;codecs=\"avc1.42e01e\"" },
      { "contentType":"video/webm;codecs=\"vp8\"" }
    ],
    "audioCapabilities": [
      { "contentType":"audio/mp4;codecs=\"mp4a.40.2\"" },
      { "contentType":"audio/webm;codecs=opus" }
    ],
    "distinctiveIdentifier":"optional",
    "persistentState":"optional",
    "sessionTypes":["temporary"]
  },
]).then(
  () => { console.log("com.microsoft.playready.software: it works"); },
  () => { console.log("com.microsoft.playready.software: it failed"); }
);
navigator.requestMediaKeySystemAccess("com.chromecast.playready", [
  {
    "initDataTypes":["cenc"],
    "videoCapabilities": [
      { "contentType": "video/mp4;codecs=\"avc1.4d401e\"" },
      { "contentType":"video/mp4;codecs=\"avc1.42e01e\"" },
      { "contentType":"video/webm;codecs=\"vp8\"" }
    ],
    "audioCapabilities": [
      { "contentType":"audio/mp4;codecs=\"mp4a.40.2\"" },
      { "contentType":"audio/webm;codecs=opus" }
    ],
    "distinctiveIdentifier":"optional",
    "persistentState":"optional",
    "sessionTypes":["temporary"]
  },
]).then(
  () => { console.log("com.chromecast.playready: it works"); },
  () => { console.log("com.chromecast.playready: it failed"); }
);
navigator.requestMediaKeySystemAccess("com.youtube.playready", [
  {
    "initDataTypes":["cenc"],
    "videoCapabilities": [
      { "contentType": "video/mp4;codecs=\"avc1.4d401e\"" },
      { "contentType":"video/mp4;codecs=\"avc1.42e01e\"" },
      { "contentType":"video/webm;codecs=\"vp8\"" }
    ],
    "audioCapabilities": [
      { "contentType":"audio/mp4;codecs=\"mp4a.40.2\"" },
      { "contentType":"audio/webm;codecs=opus" }
    ],
    "distinctiveIdentifier":"optional",
    "persistentState":"optional",
    "sessionTypes":["temporary"]
  },
]).then(
  () => { console.log("com.youtube.playready: it works"); },
  () => { console.log("com.youtube.playready: it failed"); }
);
navigator.requestMediaKeySystemAccess("com.widevine.alpha", [
  {
    "initDataTypes":["cenc"],
    "videoCapabilities": [
      { "contentType": "video/mp4;codecs=\"avc1.4d401e\"" },
      { "contentType":"video/mp4;codecs=\"avc1.42e01e\"" },
      { "contentType":"video/webm;codecs=\"vp8\"" }
    ],
    "audioCapabilities": [
      { "contentType":"audio/mp4;codecs=\"mp4a.40.2\"" },
      { "contentType":"audio/webm;codecs=opus" }
    ],
    "distinctiveIdentifier":"optional",
    "persistentState":"optional",
    "sessionTypes":["temporary"]
  },
]).then(
  () => { console.log("com.widevine.alpha: it works"); },
  () => { console.log("com.widevine.alpha: it failed"); }
);
navigator.requestMediaKeySystemAccess("com.widevine.alpha", [
  {
    "initDataTypes":["cenc"],
    "videoCapabilities": [],
    "audioCapabilities": [],
    "distinctiveIdentifier":"optional",
    "persistentState":"optional",
    "sessionTypes":["temporary"]
  },
]).then(
  () => { console.log("com.widevine.alpha legacy: it works"); },
  () => { console.log("com.widevine.alpha legacy: it failed"); }
);

Si ils sont tous en mode "NAME: it failed" -> EME non supporte
Si au moins un est en mode "NAME: it works" -> EME supporte