ssert_equals(mediaSource.activeSourceBuffers[0], sourceBufferAudio,
                            "activeSourceBuffers list only contains the audio SourceBuffer");
                          test.done();
                      });
                  });
              });
          }, "Active SourceBuffers list reflects changes to selected audio/video tracks associated with separate SourceBuffers.");


          mediasource_test(function(test, mediaElement, mediaSource)
          {
              mediaElement.addE