Detailed explanation of parsing and reading and writing audio file information using PHP (supports WMA and MP3)_PHP Tutorial

// AudioExif.class.php
// Use PHP to read and write audio file header information
// Currently only supports WMA and MP3 Two formats, only support several commonly used header information
//
// Writing information supported: Title, Artist, Copyright, Description
// Year (year), Genre (genre), AlbumTitle (album title)
// Among them, mp3 and wma are slightly different, and the specific returned information may be more, but only the above information can be written
// mp3 also supports Track (track number writing)
// For MP3 files, it supports ID3v1 and ID3v2, v2 is given priority when reading, v1 is always written when writing, and v2 is written when necessary
//
// Usage instructions: (Since wma uses Unicode access, it also needs the mb_convert_encoding() extension
// Returned data and written data are all ANSI encoding, that is, whatever is stored will be displayed (Chinese_ GB2312)
//
// require ('AudioExif.class.php');
// $AE = new AudioExif;
// $file = '/path/to/test. mp3';
//
// 1. Check whether the file is complete (only for wma, mp3 always returns true)
//
// $AE->CheckSize($file);
//
// 2. Read the information, and the return value is an array composed of the information. For the explanation of the key names, see above
//
// print_r($AE->GetInfo($file ));
//
// 3. Write information, the second parameter is a hash array, key->value, see above for support, mp3 also supports Track
// Requirements The file path of the first parameter can be written by this program
// $pa = array('Title' => 'New title', 'AlbumTitle' => 'New album name');
/ / $AE->SetInfo($file, $pa);
//
//
// Others: This plug-in spent a lot of time searching for wma and mp3 file format documentation and Web page, I hope it will be useful to everyone.
// In fact, there are many similar programs on the Internet, but there are too few for wma. It can only be operated through M$'s
// API under the win platform, and There are very few MP3s that can be operated from the unix/linux command line, so I specially wrote this module
//
// If you find a bug or submit a patch, or improve it to make it more robust, please tell me.
// (You should be able to find reference materials on the Internet about the file format and structure of ID3 and Wma)
//
if (!extension_loaded('mbstring'))
{
trigger_error ('PHP Extension module `mbstring` is required for AudioExif', E_USER_WARNING);
return true;
}
// the Main Class
class AudioExif
{
// public vars
var $_wma = false;
var $_mp3 = false;
// Construct
function AudioExif()
{
// nothing to do
}
// check the filesize
function CheckSize($file)
{
$handler = &$this->_get_handler($file);
if (!$handler) return false;
return $handler->check_size($file);
}
// get the infomations
function GetInfo($file)
{
$handler = &$this-> ;_get_handler($file);
if (!$handler) return false;
return $handler->get_info($file);
}
// write the infomations
function SetInfo($file, $pa)
{
if (!is_writable($file))
{
trigger_error('AudioExif: file `' . $file . '' can not be overwritten' , E_USER_WARNING);
return false;
}
$handler = &$this->_get_handler($file);
if (!$handler) return false;
return $handler ->set_info($file, $pa);
}
// private methods
function &_get_handler($file)
{
$ext = strtolower(strrchr($file, ' .'));
$ret = false;
if ($ext == '.mp3')
{ // MP3
$ret = &$this->_mp3;
if (!$ret) $ret = new _Mp3Exif();
}
else if ($ext == '.wma')
{ // wma
$ret = &$this ->_wma;
if (!$ret) $ret = new _WmaExif();
}
else
{ // unknown
trigger_error('AudioExif not supported `' . $ ext . '' file.', E_USER_WARNING);
}
return $ret;
}
}
// DBCS => gb2312
function dbcs_gbk($str)
{
// strip the last ""
$str = substr($str, 0, -2);
return mb_convert_encoding($str, 'GBK', 'UCS-2LE');
}
// gb2312 => DBCS
function gbk_dbcs($str)
{
  $str  = mb_convert_encoding($str, 'UCS-2LE', 'GBK');
  $str .= "";
  return $str;
}
// file exif
class _AudioExif
{
  var $fd;
  var $head;
  var $head_off;
  var $head_buf;

  // init the file handler
  function _file_init($fpath, $write = false)
  {
    $mode = ($write ? 'rb+' : 'rb');
    $this->fd = @fopen($fpath, $mode);
    if (!$this->fd)
    {
      trigger_error('AudioExif: `' . $fpath . '` can not be opened with mode `' . $mode . '`', E_USER_WARNING);
      return false;
    }
    $this->head = false;
    $this->head_off = 0;
    $this->head_buf = '';
    return true;
  }
  // read buffer from the head_buf & move the off pointer
  function _read_head_buf($len)
  {
    if ($len <= 0) return NULL;
    $buf = substr($this->head_buf, $this->head_off, $len);
    $this->head_off += strlen($buf);
    return $buf;
  }
  // read one short value
  function _read_head_short()
  {
    $ord1 = ord(substr($this->head_buf, $this->head_off, 1));
    $ord2 = ord(substr($this->head_buf, $this->head_off+1, 1));
    $this->head_off += 2;
    return ($ord1 + ($ord2<<8));
  }
  // save the file head
  function _file_save($head, $olen, $nlen = 0)
  {
    if ($nlen == 0) $nlen = strlen($head);
    if ($nlen == $olen)
    {
      // shorter
      flock($this->fd, LOCK_EX);
      fseek($this->fd, 0, SEEK_SET);
      fwrite($this->fd, $head, $nlen);
      flock($this->fd, LOCK_UN);
    }
    else
    {
      // longer, buffer required
      $stat = fstat($this->fd);
      $fsize = $stat['size'];
      // buf required (4096?) 应该不会 nlen - olen > 4096 吧
      $woff = 0;
      $roff = $olen;
      // read first buffer
      flock($this->fd, LOCK_EX);
      fseek($this->fd, $roff, SEEK_SET);
      $buf = fread($this->fd, 4096);
      // seek to start
      fseek($this->fd, $woff, SEEK_SET);
      fwrite($this->fd, $head, $nlen);
      $woff += $nlen;
      // seek to woff & write the data
      do
      {
        $buf2 = $buf;
        $roff += 4096;
        if ($roff < $fsize)
        {
          fseek($this->fd, $roff, SEEK_SET);
          $buf = fread($this->fd, 4096);       
        }
        // save last buffer
        $len2 = strlen($buf2);
        fseek($this->fd, $woff, SEEK_SET);
        fwrite($this->fd, $buf2, $len2);
        $woff += $len2;
      }
      while ($roff < $fsize);
      ftruncate($this->fd, $woff);
      flock($this->fd, LOCK_UN);
    }
  }
  // close the file
  function _file_deinit()
  {
    if ($this->fd)
    {
      fclose($this->fd);
      $this->fd = false;
    } 
  }
}
// wma class
class _WmaExif extends _AudioExif
{
  var $items1 = array('Title', 'Artist', 'Copyright', 'Description', 'Reserved');
  var $items2 = array('Year', 'Genre', 'AlbumTitle');
  // check file size (length) maybe invalid file
  function check_size($file)
  {
    $ret = false;
    if (!$this->_file_init($file)) return true;
    if ($this->_init_header())
    {
      $buf = fread($this->fd, 24);
      $tmp = unpack('H32id/Vlen/H8unused', $buf);
      if ($tmp['id'] == '3626b2758e66cf11a6d900aa0062ce6c')
      {
        $stat = fstat($this->fd);
        $ret = ($stat['size'] == ($this->head['len'] + $tmp['len']));
      }
    }
    $this->_file_deinit();
    return $ret;
  }
  // set info (save the infos)
  function set_info($file, $pa)
  {
    // check the pa
    settype($pa, 'array');
    if (!$this->_file_init($file, true)) return false;
    if (!$this->_init_header())
    {
      $this->_file_deinit();
      return false;
    }

    // parse the old header & generate the new header
    $head_body = '';
    $st_found = $ex_found = false;
    $head_num = $this->head['num'];
    while (($tmp = $this->_get_head_frame()) && ($head_num > 0))
    {
      $head_num--;
      if ($tmp['id'] == '3326b2758e66cf11a6d900aa0062ce6c')
      {  // Standard Info
        // 1-4
        $st_found = true;
        $st_body1 = $st_body2 = '';      
        $lenx = unpack('v5', $this->_read_head_buf(10));
        $tmp['len'] -= 34;  // 10 + 24
        for ($i = 0; $i < count($this->items1); $i++)
        {
          $l = $lenx[$i+1];
          $k = $this->items1[$i];
          $tmp['len'] -= $l;
          $data = $this->_read_head_buf($l);
          if (isset($pa[$k])) $data = gbk_dbcs($pa[$k]);
          $st_body2 .= $data;
          $st_body1 .= pack('v', strlen($data));
        }
        // left length
        if ($tmp['len'] > 0) $st_body2 .= $this->_read_head_buf($tmp['len']);
        // save to head_body
        $head_body .= pack('H32VH8', $tmp['id'], strlen($st_body1 . $st_body2)+24, $tmp['unused']);
        $head_body .= $st_body1 . $st_body2; 
      }
      else if ($tmp['id'] == '40a4d0d207e3d21197f000a0c95ea850')
      {  // extended info
        $ex_found = true;

        $inum = $this->_read_head_short();
        $inum2 = $inum;
        $tmp['len'] -= 26;  // 24 + 2
        $et_body = '';
        while ($tmp['len'] > 0 && $inum > 0)
        {
          // attribute name
          $nlen = $this->_read_head_short();
          $nbuf = $this->_read_head_buf($nlen);
          // the flag & value  length
          $flag = $this->_read_head_short();
          $vlen = $this->_read_head_short();
          $vbuf = $this->_read_head_buf($vlen);
          // set the length
          $tmp['len'] -= (6 + $nlen + $vlen);
          $inum--;
          // save the data?
          $name = dbcs_gbk($nbuf);
          $k = substr($name, 3);
          if (in_array($k, $this->items2) && isset($pa[$k]))
          {
            $vbuf = gbk_dbcs($pa[$k]);
            $vlen = strlen($vbuf);
            unset($pa[$k]);
          }
          $et_body .= pack('v', $nlen) . $nbuf . pack('vv', $flag, $vlen) . $vbuf;
        }
        // new tag insert??
        foreach ($this->items2 as $k)
        {
          if (isset($pa[$k]))
          {
            $inum2++;
            $nbuf = gbk_dbcs('WM/' . $k);
            $nlen = strlen($nbuf);
            $vbuf = gbk_dbcs($pa[$k]);
            $vlen = strlen($vbuf);
            $et_body .= pack('v', $nlen) . $nbuf . pack('vv', 0, $vlen) . $vbuf;
          }
        }
        // left buf?
        if ($tmp['len'] > 0) $et_body .= $this->_read_head_buf($tmp['len']);
        // save to head_body
        $head_body .= pack('H32VH8v', $tmp['id'], strlen($et_body)+26, $tmp['unused'], $inum2);
        $head_body .= $et_body; 
      }
      else
      {
        // just keep other head frame
        $head_body .= pack('H32VH8', $tmp['id'], $tmp['len'], $tmp['unused']);
        if ($tmp['len'] > 24) $head_body .= $this->_read_head_buf($tmp['len']-24);
      }
    }
    // st not found?
    if (!$st_found)
    {
      $st_body1 = $st_body2 = '';
      foreach ($this->items1 as $k)
      {
        $data = (isset($pa[$k]) ? gbk_dbcs($pa[$k]) : "");
        $st_body1 .= pack('v', strlen($data));
        $st_body2 .= $data;
      }

      // save to head_body
      $head_body .= pack('H32Va4', '3326b2758e66cf11a6d900aa0062ce6c', strlen($st_body1 . $st_body2)+24, '');
      $head_body .= $st_body1 . $st_body2;
      $this->head['num']++;
    }
    // ex not found?
    if (!$ex_found)
    {
      $inum = 0;
      $et_body = '';
      foreach ($this->items2 as $k)
      {
        $nbuf = gbk_dbcs('WM/' . $k);
        $vbuf = (isset($pa[$k]) ? gbk_dbcs($pa[$k]) : "");
        $et_body .= pack('v', strlen($nbuf)) . $nbuf . pack('vv', 0, strlen($vbuf)) . $vbuf;
        $inum++;
      }
      $head_body .= pack('H32Va4v', '40a4d0d207e3d21197f000a0c95ea850', strlen($et_body)+26, '', $inum);
      $head_body .= $et_body;
      $this->head['num']++;
    } 
    // after save
    $new_len = strlen($head_body) + 30;
    $old_len = $this->head['len'];
    if ($new_len < $old_len)
    {
      $head_body .= str_repeat("", $old_len - $new_len);
      $new_len = $old_len;
    }
    $tmp = $this->head;
    $head_buf = pack('H32VVVH4', $tmp['id'], $new_len, $tmp['len2'], $tmp['num'], $tmp['unused']);
    $head_buf .= $head_body;
    $this->_file_save($head_buf, $old_len, $new_len);
    // close the file & return
    $this->_file_deinit();
    return true;
  }
  // get info
  function get_info($file)
  {
    $ret = array();
    if (!$this->_file_init($file)) return false;
    if (!$this->_init_header())
    {
      $this->_file_deinit();
      return false;
    }
    // get the data from head_buf
    $head_num = $this->head['num'];  // num of head_frame
    while (($tmp = $this->_get_head_frame()) && $head_num > 0)
    {
      $head_num--;
      if ($tmp['id'] == '3326b2758e66cf11a6d900aa0062ce6c')
      {  // Standard Info
        $lenx = unpack('v*', $this->_read_head_buf(10));
        for ($i = 1; $i <= count($this->items1); $i++)
        {
          $k = $this->items1[$i-1];
          $ret[$k] = dbcs_gbk($this->_read_head_buf($lenx[$i]));
        }
      }
      else if ($tmp['id'] == '40a4d0d207e3d21197f000a0c95ea850')
      {  // Extended Info
        $inum = $this->_read_head_short();
        $tmp['len'] -= 26;
        while ($inum > 0 && $tmp['len'] > 0)
        {
          // attribute name
          $nlen = $this->_read_head_short();
          $nbuf = $this->_read_head_buf($nlen);
          // the flag & value  length
          $flag = $this->_read_head_short();
          $vlen = $this->_read_head_short();
          $vbuf = $this->_read_head_buf($vlen);
          // update the XX
          $tmp['len'] -= (6 + $nlen + $vlen);
          $inum--;
          $name = dbcs_gbk($nbuf);
          $k = substr($name, 3);
          if (in_array($k, $this->items2))
          {  // all is string value (refer to falg for other tags)
            $ret[$k] = dbcs_gbk($vbuf);
          }
        } 
      }
      else
      {  // skip only
        if ($tmp['len'] > 24) $this->head_off += ($tmp['len'] - 24);
      }
    }
    $this->_file_deinit();
    return $ret;
  }
  // get the header?
  function _init_header()
  {
    fseek($this->fd, 0, SEEK_SET);
    $buf = fread($this->fd, 30);
    if (strlen($buf) != 30) return false;
    $tmp = unpack('H32id/Vlen/Vlen2/Vnum/H4unused', $buf);
    if ($tmp['id'] != '3026b2758e66cf11a6d900aa0062ce6c')
      return false;
    $this->head_buf = fread($this->fd, $tmp['len'] - 30);
    $this->head = $tmp;
    return true;
  }
  // _get_head_frame()
  function _get_head_frame()
  {
    $buf = $this->_read_head_buf(24); 
    if (strlen($buf) != 24) return false;
    $tmp = unpack('H32id/Vlen/H8unused', $buf);
    return $tmp;
  }
}
// mp3 class (if not IDv2 then select IDv1)
class _Mp3Exif extends _AudioExif
{
  var $head1;
  var $genres = array('Blues','Classic Rock','Country','Dance','Disco','Funk','Grunge','Hip-Hop','Jazz','Metal','New Age','Oldies','Other','Pop','R&B','Rap','Reggae','Rock','Techno','Industrial','Alternative','Ska','Death Metal','Pranks','Soundtrack','Euro-Techno','Ambient','Trip-Hop','Vocal','Jazz+Funk','Fusion','Trance','Classical','Instrumental','Acid','House','Game','Sound Clip','Gospel','Noise','AlternRock','Bass','Soul','Punk','Space','Meditative','Instrumental Pop','Instrumental Rock','Ethnic','Gothic','Darkwave','Techno-Industrial','Electronic','Pop-Folk','Eurodance','Dream','Southern Rock','Comedy','Cult','Gangsta','Top 40','Christian Rap','Pop/Funk','Jungle','Native American','Cabaret','New Wave','Psychadelic','Rave','Showtunes','Trailer','Lo-Fi','Tribal','Acid Punk','Acid Jazz','Polka','Retro','Musical','Rock & Roll','Hard Rock','Unknown');
  // MP3 always return true
  function check_size($file)
  {
    return true;
  }
  // get info
  function get_info($file)
  {
    if (!$this->_file_init($file)) return false; 
    $ret = false;
    if ($this->_init_header())
    {
      $ret = ($this->head ? $this->_get_v2_info() : $this->_get_v1_info());
      $ret['meta'] = $this->_get_meta_info();
    }
    $this->_file_deinit();
    return $ret;
  }
  // set info
  function set_info($file, $pa)
  {
    if (!$this->_file_init($file, true)) return false;
    if ($this->_init_header())
    {
      // always save v1 info
      $this->_set_v1_info($pa);    
      // set v2 first if need
      $this->_set_v2_info($pa);
    }
    $this->_file_deinit();
    return true;
  }
  // get the header information[v1+v2], call after file_init
  function _init_header()
  {
    $this->head1 = false;
    $this->head = false;
    // try to get ID3v1 first
    fseek($this->fd, -128, SEEK_END);
    $buf = fread($this->fd, 128);
    if (strlen($buf) == 128 && substr($buf, 0, 3) == 'TAG')
    {
      $tmp = unpack('a3id/a30Title/a30Artist/a30AlbumTitle/a4Year/a28Description/CReserved/CTrack/CGenre', $buf);
      $this->head1 = $tmp;    
    }
    // try to get ID3v2
    fseek($this->fd, 0, SEEK_SET);
    $buf = fread($this->fd, 10);
    if (strlen($buf) == 10 && substr($buf, 0, 3) == 'ID3')
    {
      $tmp = unpack('a3id/Cver/Crev/Cflag/C4size', $buf);
      $tmp['size'] = ($tmp['size1']<<21)|($tmp['size2']<<14)|($tmp['size3']<<7)|$tmp['size4'];
      unset($tmp['size1'], $tmp['size2'], $tmp['size3'], $tmp['size4']);
      $this->head = $tmp;
      $this->head_buf = fread($this->fd, $tmp['size']);
    }
    return ($this->head1 || $this->head);
  }
  // get v1 info
  function _get_v1_info()
  {
    $ret = array();
    $tmpa = array('Title', 'Artist', 'Copyright', 'Description', 'Year', 'AlbumTitle');
    foreach ($tmpa as $tmp)
    {    
      $ret[$tmp] = $this->head1[$tmp];
      if ($pos = strpos($ret[$tmp], ""))
        $ret[$tmp] = substr($ret[$tmp], 0, $pos);
    }
    // count the Genre, [Track]
    if ($this->head1['Reserved'] == 0) $ret['Track'] = $this->head1['Track'];
    else $ret['Description'] .= chr($ret['Reserved']) . chr($ret['Track']);
    // Genre_idx
    $g = $this->head1['Genre'];
    if (!isset($this->genres[$g])) $ret['Genre'] = 'Unknown';
    else $ret['Genre'] = $this->genres[$g];
    // return the value
    $ret['ID3v1'] = 'yes';
    return $ret;
  }
  // get v2 info
  function _get_v2_info()
  {
    $ret = array();
    $items = array(  'TCOP'=>'Copyright', 'TPE1'=>'Artist', 'TIT2'=>'Title', 'TRCK'=> 'Track',
            'TCON'=>'Genre', 'COMM'=>'Description', 'TYER'=>'Year', 'TALB'=>'AlbumTitle');
    while (true)
    {
      $buf = $this->_read_head_buf(10);
      if (strlen($buf) != 10) break;    
      $tmp = unpack('a4fid/Nsize/nflag', $buf);
      if ($tmp['size'] == 0) break;
      $tmp['dat'] = $this->_read_head_buf($tmp['size']);
      // 0x6000 (11000000 00000000) 
      if ($tmp['flag'] & 0x6000) continue;
      // mapping the data
      if ($k = $items[$tmp['fid']])
      {  // If first char is "", just skip
        if (substr($tmp['dat'], 0, 1) == "") $tmp['dat'] = substr($tmp['dat'], 1);
        $ret[$k] = $tmp['dat'];
      }
    }
    // reset the genre
    if ($g = $ret['Genre'])
    {
      if (substr($g,0,1) == '(' && substr($g,-1,1) == ')') $g = substr($g, 1, -1);
      if (is_numeric($g))
      {
        $g = intval($g);
        $ret['Genre'] = (isset($this->genres[$g]) ? $this->genres[$g] : 'Unknown');
      }
    }
    $ret['ID3v1'] = 'no';
    return $ret;
  }
  // get meta info of MP3
  function _get_meta_info()
  {
    // seek to the lead buf: 0xff
    $off = 0;
    if ($this->head) $off = $this->head['size'] + 10;
    fseek($this->fd, $off, SEEK_SET);
    while (!feof($this->fd))
    {
      $skip = ord(fread($this->fd, 1));
      if ($skip == 0xff) break;
    }
    if ($skip != 0xff) return false;
    $buf = fread($this->fd, 3);
    if (strlen($buf) != 3) return false;
    $tmp = unpack('C3', $buf);
    if (($tmp[1] & 0xf0) != 0xf0) return false;
    // get the meta info
    $meta = array();
    // get mpeg version
    $meta['mpeg']  = ($tmp[1] & 0x08 ? 1 : 2);
    $meta['layer']  = ($tmp[1] & 0x04) ? (($tmp[1] & 0x02) ? 1 : 2) : (($tmp[1] & 0x02) ? 3 : 0);
    $meta['epro']  = ($tmp[1] & 0x01) ? 'no' : 'yes';
    // bit rates
    $bit_rates = array(
      1 => array(
        1 => array(0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,0),
        2 => array(0,32,48,56,64,80,96,112,128,160,192,224,256,320,384,0),
        3 => array(0,32,40,48,56,64,80,96,112,128,160,192,224,256,320,0)
      ),
      2 => array(
        1 => array(0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,0),
        2 => array(0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0),
        3 => array(0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0)
      )
    );
    $i = $meta['mpeg'];
    $j = $meta['layer'];
    $k = ($tmp[2]>>4);
    $meta['bitrate'] = $bit_rates[$i][$j][$k];
    // sample rates <采样率>
    $sam_rates = array(1=>array(44100,48000,32000,0), 2=>array(22050,24000,16000,0));
    $meta['samrate'] = $sam_rates[$i][$k];
    $meta["padding"] = ($tmp[2] & 0x02) ? 'on' : 'off';
    $meta["private"] = ($tmp[2] & 0x01) ? 'on' : 'off';
    // mode & mode_ext
    $k = ($tmp[3]>>6);
    $channel_modes = array('stereo', 'joint stereo', 'dual channel', 'single channel');
    $meta['mode'] = $channel_modes[$k];
    $k = (($tmp[3]>>4) & 0x03);
    $extend_modes = array('MPG_MD_LR_LR', 'MPG_MD_LR_I', 'MPG_MD_MS_LR', 'MPG_MD_MS_I');
    $meta['ext_mode'] = $extend_modes[$k];
    $meta['copyright'] = ($tmp[3] & 0x08) ? 'yes' : 'no';
    $meta['original'] = ($tmp[3] & 0x04) ? 'yes' : 'no';
    $emphasis = array('none', '50/15 microsecs', 'rreserved', 'CCITT J 17');
    $k = ($tmp[3] & 0x03);
    $meta['emphasis'] = $emphasis[$k];
    return $meta;
  }
  // set v1 info
  function _set_v1_info($pa)
  {
    // ID3v1 (simpled)
    $off = -128;
    if (!($tmp = $this->head1))
    {    
      $off = 0;
      $tmp['id'] = 'TAG';
      $tmp['Title'] = $tmp['Artist'] = $tmp['AlbumTitle'] = $tmp['Year'] = $tmp['Description'] = '';
      $tmp['Reserved'] = $tmp['Track'] = $tmp['Genre'] = 0;
    }

    // basic items
    $items = array('Title', 'Artist', 'Copyright', 'Description', 'Year', 'AlbumTitle');
    foreach ($items as $k)
    {
      if (isset($pa[$k])) $tmp[$k] = $pa[$k];
    }
    // genre index
    if (isset($pa['Genre']))
    {
      $g = 0;
      foreach ($this->genres as $gtmp)
      {
        if (!strcasecmp($gtmp, $pa['Genre']))
          break;
        $g++;
      }
      $tmp['Genre'] = $g;
    }
    if (isset($pa['Track'])) $tmp['Track'] = intval($pa['Track']);
    // pack the data
    $buf = pack('a3a30a30a30a4a28CCC',  $tmp['id'], $tmp['Title'], $tmp['Artist'], $tmp['AlbumTitle'],
            $tmp['Year'], $tmp['Description'], 0, $tmp['Track'], $tmp['Genre']);
    flock($this->fd, LOCK_EX);
    fseek($this->fd, $off, SEEK_END);
    fwrite($this->fd, $buf, 128);
    flock($this->fd, LOCK_UN);
  }
  // set v2 info
  function _set_v2_info($pa)
  {
    if (!$this->head)
    {  // insert ID3
      return;  // 没有就算了
      /**
      $tmp = array('id'=>'ID3','ver'=>3,'rev'=>0,'flag'=>0);
      $tmp['size'] = -10;  // +10 => 0
      $this->head = $tmp;
      $this->head_buf = '';
      $this->head_off = 0;
      **/
    }
    $items = array(  'TCOP'=>'Copyright', 'TPE1'=>'Artist', 'TIT2'=>'Title', 'TRAC'=>'Track',
            'TCON'=>'Genre', 'COMM'=>'Description', 'TYER'=>'Year', 'TALB'=>'AlbumTitle');
    $head_body = '';
    while (true)
    {
      $buf = $this->_read_head_buf(10);
      if (strlen($buf) != 10) break;
      $tmp = unpack('a4fid/Nsize/nflag', $buf);
      if ($tmp['size'] == 0) break;
      $data = $this->_read_head_buf($tmp['size']);
      if (($k = $items[$tmp['fid']]) && isset($pa[$k]))
      {
        // the data should prefix by "" [replace]
        $data = "" . $pa[$k];
        unset($pa[$k]);
      }
      $head_body .= pack('a4Nn', $tmp['fid'], strlen($data), $tmp['flag']) . $data;
    }
    // reverse the items & set the new tags
    $items = array_flip($items);
    foreach ($pa as $k => $v)
    {
      if ($fid = $items[$k])
      {
        $head_body .= pack('a4Nn', $fid, strlen($v) + 1, 0) . "" . $v;
      }
    }
    // new length
    $new_len = strlen($head_body) + 10;
    $old_len = $this->head['size'] + 10;
    if ($new_len < $old_len)
    {
      $head_body .= str_repeat("", $old_len - $new_len);
      $new_len = $old_len;    
    }
    // count the size1,2,3,4, no include the header
    // 较为变态的算法... :p (28bytes integer)
    $size = array();
    $nlen = $new_len - 10;
    for ($i = 4; $i > 0; $i--)
    {
      $size[$i] = ($nlen & 0x7f);
      $nlen >>= 7;
    }
    $tmp = $this->head;
    //echo "old_len : $old_len new_len: $new_len ";
    $head_buf = pack('a3CCCCCCC', $tmp['id'], $tmp['ver'], $tmp['rev'], $tmp['flag'],
      $size[1], $size[2], $size[3], $size[4]);
    $head_buf .= $head_body;
    $this->_file_save($head_buf, $old_len, $new_len);
  }
}
?>