读取MP3详情信息

做之前,都没有想到读取MP3额外信息竟然如此简单,看来有时候技术真的就是一层玻璃纸,捅破了就没有什么秘密感.

类ExtractMusic:

public class ExtractMusic {

    public static void main(String[] args) throws IOException {

        //就用梁静茹的歌做个示例

        String path = new String("d://慢慢来比较快.mp3");

        /**

         * RandomAccessFile(String name, String mode) 

         * 

         * name:指定文件,不用多说了

         * mode:访问模式("r"、"rw"、"rws" 或 "rwd" ),"r"代表只读

         */

        RandomAccessFile read = new RandomAccessFile(path, "r");

        /**

         * public void seek(long pos)  throws IOException

         * pos:文件指针偏移量

         * MP3的最后128个字节用来存储额外信息,详情请看

         * (http://mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm#MPEGTAG)

         */

        read.seek(read.length()-128);    //将文件指针定位到最后128个字节的位置,准备读取

        byte[] buffer = new byte[128];    //准备存储最后128个字节

        /**

         * public final void readFully(byte[] b)  throws IOException

         * b:从当前文件指针开始,将 b.length 个字节读到 b中

         */

        read.readFully(buffer);

        MusicInfo info = new MusicInfo(buffer);//用MusicInfo类来封装buffer的数据

        if(info.isValid()){    //判断数据的合法性,以及封装数据

            System.out.println("title:" + info.getTitle());

            System.out.println("artist:" + info.getArtist());

            System.out.println("album:" + info.getAlbum());

            System.out.println("year:"  + info.getYear());

            System.out.println("comment:" + info.getComment());

            //在MusicInfo中,虽然有genre的成员,但是并没有给其数据,所以输出为null

            System.out.println(info.getGenre());

        }

        /**

              输出:

                 title:慢慢来比较快

                artist:梁静茹

                album:情歌没有告诉你

                year:2010

                comment:WWW.TOP100.CN 巨鲸音乐网

                null

         */

    }

} 

类MusicInfo:

 

public class MusicInfo {

    private final String TAG = "TAG";

    private String title;

    private String artist;

    private String album;

    private String year;

    private String comment;

    private String genre;

    private byte[] buffer = null;

    public MusicInfo() {}

    public MusicInfo(byte[] buffer) { 

        this.buffer = buffer; //接受buffer

    }

    public boolean isValid() throws UnsupportedEncodingException{

        /**

          http://mpgedit.org/mpgedit/mpeg_format/mpeghdr.htm#MPEGTAG

          MP3格式最后128个字节存储方式,

            Sign    Length

            (bytes)    Position

            (bytes)    Description

            A    3    (0-2)    Tag identification. Must contain 'TAG' if tag exists and is correct.

            B    30    (3-32)    Title

            C    30    (33-62)    Artist

            D    30    (63-92)    Album

            E    4    (93-96)    Year

            F    30    (97-126)    Comment

            G    1    (127)    Genre

          由于规定前3个字节是TAG,所以如果只想简单的校验数据,只需判断TAG是否存在就行了

         */

        String flag = new String(this.buffer,0,3);

        if(TAG.equals(flag)){        //如果存在,封装数据

            /**

              中文歌曲,而且额外信息中也包含中文,需要手动用gb18030编码,详情请看:

              http://baike.baidu.com/view/889058.htm

             */

            this.title = new String(this.buffer,3,30,"gb18030").trim();

            this.artist = new String(this.buffer,33,30,"gb18030").trim();

            this.album = new String(this.buffer,63,30,"gb18030").trim();

            this.year = new String(this.buffer,93,4,"gb18030").trim();

            this.comment = new String(this.buffer,97,30,"gb18030").trim();

            /**

               没有对genre成员赋值,因为这1个字节里面存的不是流派的直接值,类似于索引值

                0    'Blues'    20    'Alternative'    40    'AlternRock'    60    'Top 40'

                1    'Classic Rock'    21    'Ska'    41    'Bass'    61    'Christian Rap'

                2    'Country'    22    'Death Metal'    42    'Soul'    62    'Pop/Funk'

                3    'Dance'    23    'Pranks'    43    'Punk'    63    'Jungle'

                4    'Disco'    24    'Soundtrack' ...

                ...

                这里就不进行处理了

             */

            //this.genre = this.buffer[127];

            return true;

        }

        return false;

    }

    public String getTitle() {

        return title;

    }

    public String getArtist() {

        return artist;

    }

    public String getAlbum() {

        return album;

    }

    public String getYear() {

        return year;

    }

    public String getComment() {

        return comment;

    }

    public String getGenre() {

        return genre;

    }

}