MP4 is indicated for M4A files

[Thomas Lidy]

Pure .m4a audio files show MP4 as file extension:

    with open(full_file, "rb") as f:
        info = fleep.get(f.read(128))

    print(info.type, info.extension, info.mime, file)

['video'] ['mp4'] ['video/mp4'] Bob Marley & The Wailers - Jamming-VF30VS5FZ6c.m4a