How to use the essentia.standard.YamlOutput function in essentia

jam = jams2.load(file_struct.ref_file)

        # If beat annotations exist, compute also annotated beatsyn features
        if jam.beats != []:
            logging.info("Reading beat annotations from JAMS")
            annot = jam.beats[0]
            annot_beats = []
            for data in annot.data:
                annot_beats.append(data.time.value)
            annot_beats = essentia.array(np.unique(annot_beats).tolist())
            annot_mfcc, annot_hpcp, annot_tonnetz = compute_features(
                audio, annot_beats)

    # Save output as json file
    logging.info("Saving the JSON file in %s" % out_file)
    yaml = YamlOutput(filename=out_file, format='json')
    pool = essentia.Pool()
    pool.add("beats.times", features["beats"])
    pool.add("beats.confidence", features["beats_conf"])
    pool.set("analysis.sample_rate", msaf.Anal.sample_rate)
    pool.set("analysis.frame_rate", msaf.Anal.frame_size)
    pool.set("analysis.hop_size", msaf.Anal.hop_size)
    pool.set("analysis.window_type", msaf.Anal.window_type)
    pool.set("analysis.mfcc_coeff", msaf.Anal.mfcc_coeff)
    pool.set("timestamp",
             datetime.datetime.today().strftime("%Y/%m/%d %H:%M:%S"))
    save_features("framesync", pool, features["mfcc"], features["hpcp"],
                  features["tonnetz"])
    save_features("est_beatsync", pool, features["bs_mfcc"],
                  features["bs_hpcp"], features["bs_tonnetz"])
    if os.path.isfile(file_struct.ref_file) and jam.beats != []:
        save_features("ann_beatsync", pool, annot_mfcc, annot_hpcp,