Event(sourceBuffer.audioTracks, "change");
                      sourceBuffer.audioTracks[0].enabled = false;
                  });

                  test.waitForExpectedEvents(function()
                  {
                      assert_equals(mediaSource.activeSourceBuffers.length, 1,
                        "activeSourceBuffers list unchanged");

                      test.expectEvent(sourceBuffer.videoTracks, "change");
                      sourceBuffer.audioTracks[0].enabled = true;
                  