content: import argparse
  import glob
  import os
  import os.path as osp
  from multiprocessing import Pool
  
  import mmcv
  
  
  def extract_audio_wav(line):
      """Extract the audio wave from video streams using FFMPEG."""
      video_id, _ = osp.splitext(osp.basename(line))
      video_dir = osp.dirname(line)
      video_rel_dir = osp.relpath(video_dir, args.root)
      dst_dir = osp.join(args.dst_root, video_rel_dir)
      os.popen(f'mkdir -p {dst_dir}')
      try:
          if osp.exists(f'{dst_dir}/{video_id}.wav'):
              return
          cmd = f'ffmpeg -i ./{line}  -map 0:a  -y {dst_dir}/{video_id}.wav'
          os.popen(cmd)
      except BaseException:
          with open('extract_wav_err_file.txt', 'a+') as f:
              f.write(f'{line}\n')
  
  
  def parse_args():
      parser = argparse.ArgumentParser(description='Extract audios')
      parser.add_argument('root', type=str, help='source video directory')
      parser.add_argument('dst_root', type=str, help='output audio directory')
      parser.add_argument(
          '--level', type=int, default=2, help='directory level of data')
      parser.add_argument(
          '--ext',
          type=str,
          default='mp4',
          choices=['avi', 'mp4', 'webm'],
          help='video file extensions')
      parser.add_argument(
          '--num-worker', type=int, default=8, help='number of workers')
      args = parser.parse_args()
  
      return args
  
  
  if __name__ == '__main__':
      args = parse_args()
  
      mmcv.mkdir_or_exist(args.out_dir)
  
      print('Reading videos from folder: ', args.src_dir)
      print('Extension of videos: ', args.ext)
      fullpath_list = glob.glob(args.src_dir + '/*' * args.level + '.' +
                                args.ext)
      done_fullpath_list = glob.glob(args.out_dir + '/*' * args.level + '.wav')
      print('Total number of videos found: ', len(fullpath_list))
      print('Total number of videos extracted finished: ',
            len(done_fullpath_list))
  
      pool = Pool(args.num_worker)
      pool.map(extract_audio_wav, fullpath_list)
  