Java 获取amr音频格式的音频长度

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

public class GetAmrDuration {

    /**
     * 得到amr的时长
     * 
     * @param file
     * @return
     * @throws IOException
     */
    public static int 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();// 文件的长度
            int pos = 6;// 设置初始位置
            int frameCount = 0;// 初始帧数
            int packedPos = -1;

            byte[] datas = new byte[1];// 初始数据值
            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;// 帧数*20
        } finally {
            if (randomAccessFile != null) {
                randomAccessFile.close();
            }
        }
        return (int)((duration/1000)+1);
    }
    
    public static void main(String[] args) throws IOException {
        File source = new File("6.amr");
        System.out.println(getAmrDuration(source));
    }

}