e.activeSourceBuffers.length, 0,
                    "activeSourceBuffers is empty to start with");

                  test.expectEvent(mediaSource.activeSourceBuffers, "addsourcebuffer");
                  test.expectEvent(mediaElement, "loadedmetadata");
                  sourceBuffer.appendBuffer(dataVideo);

                  test.waitForExpectedEvents(function()
                  {
                      assert_equals(mediaSource.activeSourceBuffers.length, 1,
                        "activeSourceBuffer