pip install --user vtt_to_srt

 python vtt_to_srt.py pathname [-r]
    
    pathname - a file or directory with files to be converted 
    
    -r       - walk path recursively                          

 # convert vtt file
    
    from vtt_to_srt import vtt_to_srt
    path = '/path/to/file.vtt'
    vtt_to_srt(path)
    
    
    # recursively convert all vtt files in directory
    
    from vtt_to_srt import vtts_to_srt
    path = '/path/to/directory'
    vtts_to_srt(path, rec = True)