/**
     * 得到amr的時長
     * 
     * @param file
     * @return
     * @throws IOException
     */
    public static long getAmrDuration(File file) throws IOException {
        long duration = -1;
        int[] packedSize = { 12, 13, 15, 17, 19, 20, 26, 31, 5, 0, 0, 0, 0, 0, 0, 0 };
        RandomAccessFile randomAccessFile = null;
        try {
            randomAccessFile = new RandomAccessFile(file, "rw");
            long length = file.length();//檔案的長度
            int pos = 6;//設定初始位置
            int frameCount = 0;//初始幀數
            int packedPos = -1;
            /////////////////////////////////////////////////////
            byte[] datas = new byte[1];//初始資料值
            while (pos <= length) {
                randomAccessFile.seek(pos);
                if (randomAccessFile.read(datas, 0, 1) != 1) {
                    duration = length > 0 ? ((length - 6) / 650) : 0;
                    break;
                }
                packedPos = (datas[0] >> 3) & 0x0F;
                pos += packedSize[packedPos] + 1;
                frameCount++;
            }
            /////////////////////////////////////////////////////
            duration += frameCount * 20;//幀數*20
        } finally {
            if (randomAccessFile != null) {
                randomAccessFile.close();
            }
        }
        return duration;
    }