def ffmpeg_middle(ext_to):
    """
    Function to get ffmpeg command middle section to convert to a given
    file extension.
    
    Parameter
    ---------
    ext_to: string
        filetype to convert to
        
    Returns
    -------
    ffmiddle: string
        ffmpeg command middle section
    """
    ffmiddles = {
        "mp3": " -codec:a libmp3lame -ac 2 -qscale:a 2 ",
        "wav": " -ac 2 -acodec pcm_s16le "
    }
    return(ffmiddles[ext_to.lower()])