@classmethod
def __find_mp3_start__(cls, mp3file):
    """places mp3file at the position of the MP3 file's start"""
    from audiotools.id3 import skip_id3v2_comment
    skip_id3v2_comment(mp3file)
    from audiotools.bitstream import BitstreamReader
    reader = BitstreamReader(mp3file, False)
    pos = reader.getpos()
    frame_sync, mpeg_id, layer = reader.parse('11u 2u 2u 1p')
    while not (frame_sync == 2047 and mpeg_id in (0, 2, 3) and layer in (1,
        2, 3)):
        reader.setpos(pos)
        reader.skip(8)
        pos = reader.getpos()
    reader.setpos(pos)
