PHP学习：php实现将wav文件转换成图像文件并在页面中显示的方法

<?php
 function wav_graph($file, $f=0, $w=0)
 {
  global $DATA_DIR;
  if(!is_file($file))
   return 0;
  $fp = fopen($DATA_DIR.$file, 'r');
  $raw = fread($fp, 36);
  $str = '';
  $header = unpack('A4Riff/VSize/A4Wav/A4Head/VHeadSize/vPCM/vChannels/VSampleRate/VByteRate/vBlockAlign/vSampleBits', $raw);
  foreach($header as $k=>$v)
   $str .= $k.': '. $v.' ';
  fseek($fp, 36 + $header['HeadSize'] - 16);
  $raw = fread($fp, 8);
  $data = unpack('A4Data/VDataSize', $raw);
  foreach($data as $k=>$v)
   $str .= $k.': '. $v.' ';
  $b = $header['SampleBits'];
  $c = $header['Channels'];
  $l = $b * $c / 8; // sample frame length in bytes
  $s = $data['DataSize'] / $l; // total number of samples
  $r = $header['SampleRate'];
  if($f)
   $h = pow(2, $b) / $f;
  else
   { $h = 200; $f = pow(2, $b - 1) / $h; }
  if($w == 0)
   $w = round($r / 1000); // default to show 1k sample frames per minute
  header("Content-type: image/png");
  $im = imagecreate($s / $w, $h * $c * 2);
  imagecolorallocate($im, 0xff, 0xff, 0xff); // white bg
  $color = imagecolorallocate($im, 0, 0, 255); // black
  imagestring($im, 5, 5, 5, $str, $color);
  $x=0; $y = array(); $yn = array();
  for($i = 0; $i < $c; $i++) $y[$i] = $h * $i + $h;
  $n = $l * $w;
  while(1)
  {
   if($s == 0) 
    break;
   if($s < $n) 
    $n = $s;
   $samples = fread($fp, 1000 * $n);
   if($samples === FALSE)
    break;
   $packed = unpack("s*", $samples);
   foreach($packed as $k=>$v)
   {
    $cnt = ($k-1) % ($w * $l) ;
    if( $cnt > $c - 1) 
     continue;
    $yn[$cnt] = $h * $cnt + $h - $v / $f;
    imageline($im, $x, $y[$cnt], $x+1, $yn[$cnt], $color);
    $y[$cnt] = $yn[$cnt];
    $x++;
   }
   $s -= $n;
  }
  imagepng($im);
  imagedestroy($im);
 }
 wav_graph('GetWave.wav');
?>