--- a/dom/webidl/HTMLMediaElement.webidl
+++ b/dom/webidl/HTMLMediaElement.webidl
@@ -215,16 +215,24 @@ partial interface HTMLMediaElement {
 partial interface HTMLMediaElement {
   [Pref="media.test.video-suspend"]
   void setVisible(boolean aVisible);
 
   [Pref="media.test.video-suspend"]
   boolean hasSuspendTaint();
 };
 
+/* Audio Output Devices API */
+partial interface HTMLMediaElement {
+  [Pref="media.setsinkid.enabled"]
+  readonly attribute DOMString sinkId;
+  [Throws, Pref="media.setsinkid.enabled"]
+  Promise<void> setSinkId(DOMString sinkId);
+};
+
 /*
  * API that exposes whether a call to HTMLMediaElement.play() would be
  * blocked by autoplay policies; whether the promise returned by play()
  * would be rejected with NotAllowedError.
  */
 partial interface HTMLMediaElement {
   [Pref="media.allowed-to-play.enabled"]
   readonly attribute boolean allowedToPlay;