nd active SourceBuffer matches second SourceBuffer");
                              test.done();
                          });
                      });
                  });
              },
              "Active SourceBuffers must appear in the same order as they appear in the sourceBuffers attribute: " +
                (addAudioFirst ? "audio is first sourceBuffer" : "video is first sourceBuffer") + ", " +
                (appendAudioFirst ? "audio media appended first" : "video media appended first"));