fix: Don't update captions when video is paused (#6474)

This avoids wasting processing resources when it is not necessary

lib/text/ui_text_displayer.js

@@ -72,7 +72,9 @@ shaka.text.UITextDisplayer = class {
 
     /** @private {shaka.util.Timer} */
     this.captionsTimer_ = new shaka.util.Timer(() => {
-      this.updateCaptions_();
+      if (!this.video_.paused) {
+        this.updateCaptions_();
+      }
     }).tickEvery(updatePeriod);
 
     /**
@@ -93,6 +95,10 @@ shaka.text.UITextDisplayer = class {
       this.updateCaptions_(/* forceUpdate= */ true);
     });
 
+    this.eventManager_.listen(this.video_, 'seeking', () => {
+      this.updateCaptions_(/* forceUpdate= */ true);
+    });
+
     // From: https://html.spec.whatwg.org/multipage/media.html#dom-video-videowidth
     // Whenever the natural width or natural height of the video changes
     // (including, for example, because the selected video track was changed),