(function()
                  {
                      assert_equals(mediaSource.activeSourceBuffers.length, 1,
                        "activeSourceBuffers list updated when tracks are loaded");
                      assert_equals(sourceBuffer.audioTracks.length, 1,
                        "audio track list contains loaded audio track");
                      assert_equals(sourceBuffer.videoTracks.length, 1,
                        "video track list contains loaded video track");

                      medi