how to convert librosa method

[sa-a-an]

Hi, i have issue with converting librosa method to onnx.
I used skl2onnx libary but need to write custom canculator and convertor either of example didnt work, maybe some one could give some advice.
Example of code:

class FetureExtractor(TransformerMixin, BaseEstimator):

    def __init__(self, X = None, alpha=0.):
        self.mult_coeff = 2
        self._mel = np.ones((1,16,8,1))

    def fit(self, X, y = None):
        print("-----fit TestFeatureExtractor-----")
        return self 


    def transform(self, X, sample_rate = 22050):
        # We extract mfcc feature from data
        mels = np.mean(librosa.feature.melspectrogram(y=X, sr=sample_rate).T,axis=0)
        self._mel = mels.reshape(1,16,8,1)

        return self._mel

def test_feature_extractor_calculator(operator):
    op = operator.raw_operator
    input_type = operator.inputs[0].type.__class__

    input = operator.inputs[0]      # inputs in ONNX graph
    N = input.type.shape[0]
    print(operator.inputs[0].type)

    input_dim = operator.inputs[0].get_first_dimension()
    print(input_dim)
    operator.outputs[0].type = FloatTensorType((1,16,8,1))

def test_feature_extractor_converter(scope, operator, container):
    op = operator.raw_operator
    opv = container.target_opset
    out = operator.outputs
    X = operator.inputs[0]
    print('X {}'.format(X))
    dtype = guess_numpy_type(X.type)

    N = 20        # number of observations
    C = 20   # dimension of outputs
    coef = np.full((1,16,8,1), op.mult_coeff).astype(dtype)
    Y = OnnxMatMul(X,coef, op_version=opv, output_names=out[:1])
    Y.add_to(scope, container)