Add DRM check for Chrome

src/ext/lib/ar-detect/ArDetector.js

@@ -38,6 +38,9 @@ class ArDetector {
     this._nextTick = false;
 
     this.canDoFallbackMode = false; 
+
+    this.drmNotificationShown = false;
+
     this.logger.log('info', 'init', `[ArDetector::ctor] creating new ArDetector. arid: ${this.arid}`);
   }
 
@@ -506,6 +509,25 @@ class ArDetector {
     id = undefined;
   }
 
+  /**
+   * Checks whether video we're trying to play is protected by DRM. 
+   * 
+   * When trying to get an image frame of a DRM-protected video in
+   * firefox, the method canvas.drawImage(video) will throw an exception.
+   * 
+   * This doesn't happen in Chrome. As opposed to Firefox, chrome will
+   * simply draw a transparent black image and not tell anyone that
+   * anything is amiss. However, since the image is (according to my testing
+   * on netflix) completely transparent, this means we can determine whether
+   * the video is DRM-protected by looking at the alpha byte of the image.
+   * 
+   * (Videos don't tend to have an alpha channel, so they're always
+   * completely opaque (i.e. have value of 255))
+   */
+  hasDRM() {
+    return this.blackframeContext.getImageData(0,0,1,1).data[3] === 0;
+  }
+
   frameCheck(){
     if(! this.video){
       this.logger.log('error', 'debug', `%c[ArDetect::frameCheck] <@${this.arid}>  Video went missing. Destroying current instance of videoData.`);
@@ -525,12 +547,19 @@ class ArDetector {
     //
     try {
       this.blackframeContext.drawImage(this.video, 0, 0, this.blackframeCanvas.width, this.blackframeCanvas.height);
+
+      // special browsers require special tests
+      if (this.hasDRM()) {
+        throw 'Video is protected by DRM. Autodetection cannot run here.';
+      }
       this.fallbackMode = false;
     } catch (e) {
       this.logger.log('error', 'arDetect', `%c[ArDetect::frameCheck] <@${this.arid}>  %c[ArDetect::frameCheck] can't draw image on canvas. ${this.canDoFallbackMode ? 'Trying canvas.drawWindow instead' : 'Doing nothing as browser doesn\'t support fallback mode.'}`, "color:#000; backgroud:#f51;", e);
 
       // nothing to see here, really, if fallback mode isn't supported by browser
-      if (! this.canDoFallbackMode) {
+      if (!this.drmNotificationShown) {
+        this.drmNotificationShown = true;
+        this.conf.player.showNotification('AARD_DRM');
         return;
       }
       if (! this.canvasReadyForDrawWindow()) {