如何读取文件夹和子文件夹*.wav；以及用于输入训练模型的特征提取？

import os

def read_wav_files(folder_path):
    wav_files = []
    for root, dirs, files in os.walk(folder_path):
        for file in files:
            if file.endswith(".wav"):
                wav_files.append(os.path.join(root, file))
    return wav_files

folder_path = "/path/to/folder"
wav_files = read_wav_files(folder_path)
print(wav_files)

import librosa

def extract_mel_spectrogram(file_path):
    audio, sr = librosa.load(file_path)
    mel_spectrogram = librosa.feature.melspectrogram(audio, sr=sr)
    return mel_spectrogram

file_path = "/path/to/wav_file.wav"
mel_spectrogram = extract_mel_spectrogram(file_path)
print(mel_spectrogram)