                 expectedSecondSB = sourceBufferAudio = mediaSource.addSourceBuffer(typeAudio);
                          }

                          assert_equals(mediaSource.activeSourceBuffers.length, 0,
                            "activeSourceBuffers is empty to start with");
                          assert_equals(mediaSource.sourceBuffers.length, 2,
                            "sourceBuffers list contains both SourceBuffers");
                          assert_equals(mediaSource.sourceBuffers[0], exp