I tried one of the W3C EME tests that check readyState locally (https://web-platform.test:8443/encrypted-media/drm-mp4-playback-temporary-multikey-sequential-readyState.html). With the test changed as listed below, it passes. The change basically waits 4 seconds before checking readyState. However, there was a complication in that the test only expects 1 timeupdate event, but the video "plays" a couple of seconds before stalling (thus you get several timeupdate events). I had to disable the asserts for that part of the test as well.

Once this is fixed to change the readyState immediately then this W3C test should pass as it is currently written.

--- a/encrypted-media/scripts/playback-temporary-multikey-sequential.js
+++ b/encrypted-media/scripts/playback-temporary-multikey-sequential.js
@@ -57,13 +57,16 @@ function runTest(config,qualifier) {
         }
 
         function onWaitingForKey(event) {
-            _waitingForKey = true;
             if (config.checkReadyState) {
                 // This test does not start playing until the first license has been provided,
                 // so this event should occur when transitioning between keys.
                 // Thus, the frame at the current playback position is available and readyState
                 // should be HAVE_CURRENT_DATA.
-                assert_equals(_video.readyState, _video.HAVE_CURRENT_DATA,
-                    "Video readyState should be HAVE_CURRENT_DATA on watingforkey event");
+                test.step_timeout(function() { 
+                    _waitingForKey = true;
+                    assert_equals(_video.readyState, _video.HAVE_CURRENT_DATA,
+                        "Video readyState should be HAVE_CURRENT_DATA on watingforkey event");
+                }, 4000);
             }
             startNewSession();
         }
@@ -87,13 +90,13 @@ function runTest(config,qualifier) {
             // the new ready state is HAVE_CURRENT_DATA or less" case of the readyState change
             // algorithm which requires a "timeupdate" event be fired.
              if (_waitingForKey) {
-                assert_equals(++_timeupdateWhileWaitingCount, 1, "Should only receive one timeupdate while waiting for key");
                 assert_equals(_video.readyState, _video.HAVE_CURRENT_DATA, "Video readyState should be HAVE_CURRENT_DATA while wating for key");
             }
 
             if (_video.currentTime > config.duration) {
                 assert_equals(_mediaKeySessions.length, config.initData.length, "It should require all keys to reach end of content");
-                assert_equals(_timeupdateWhileWaitingCount, 1, "Should have only received exactly one timeupdate while waiting for key");
                 _video.pause();
                 test.done();
             }

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