  "activeSourceBuffers updated when media element is loaded");
                      assert_equals(mediaSource.activeSourceBuffers[0], sourceBuffer,
                        "activeSourceBuffers contains sourceBuffer when media element is loaded");
                      test.done();
                  });
              });
          }, "SourceBuffer added to activeSourceBuffers list when its only audio track gets loaded (and thus becomes enabled).");


          mediasource_test(function(test, mediaElement, m