Peter's Useful Crap

One of the new features of my anti-spam plugin is the ability to create auto-generated mp3 files. The plugin concatenates individual mp3 files representing the sound of each letter in the alphabet, in order to build a word.

Of course, I have no idea how to code something that merges mp3 files, so I had to do some searching and eventually found this site with some working code: http://www.sourcerally.net/Scripts/20-PHP-MP3-Class.

Here is my modified version, with some simplified functionality (I removed the code that added ID3 tags) and an added feature that I modified from FPDF (a script that creates PDFs in PHP) in order to output (to the browser) the merged mp3 file, prompting users to open or save it. This code is compatible with both PHP 4 and PHP 5.

<?php
// This is the class to generate mp3 files based on the anti-spam words
// Based on the PHP mp3 class at http://www.sourcerally.net/Scripts/20-PHP-MP3-Class
// Output code based on the FPDF class at http://www.fpdf.org
class mp3
  {
  	var $str;
  	var $time;
  	var $frames;

  	// Create a new mp3
  	function mp3($path="")
  	{
  	if($path!="")
  		{
  		$this->str = file_get_contents($path);
  		}
  	}

  // Put an mp3 behind the first mp3
  function mergeBehind($mp3)
  {
  $this->str .= $mp3->str;
  }

  // Calculate where's the end of the sound file
  function getIdvEnd()
  {
  $strlen = strlen($this->str);
  $str = substr($this->str,($strlen-128));
  $str1 = substr($str,0,3);
  if(strtolower($str1) == strtolower('TAG'))
  {
  return $str;
  }
  else
  {
  return false;
  }
  }

  // Calculate where's the beginning of the sound file
  function getStart()
  {
  $strlen = strlen($this->str);
  for($i=0;$i<$strlen;$i++)
  {
  $v = substr($this->str,$i,1);
  $value = ord($v);
  if($value == 255)
  {
  return $i;
  }
  }
  }

  // Remove the ID3 tags
  function striptags()
  {
  //Remove start stuff...
  $newStr = '';
  $s = $start = $this->getStart();
  if($s===false)
  {
  return false;
  }
  else
  {
  $this->str = substr($this->str,$start);
  }
  //Remove end tag stuff
  $end = $this->getIdvEnd();
  if($end!==false)
  {
  $this->str = substr($this->str,0,(strlen($this->str)-129));
  }
  }

  // Display an error
  function error($msg)
  {
  //Fatal error
  die('<strong>audio file error: </strong>'.$msg);
  }

 // Send the new mp3 to the browser
  function output($path)
  {
  //Output mp3
  //Send to standard output
  if(ob_get_contents())
  $this->error('Some data has already been output, can\'t send mp3 file');
  if(php_sapi_name()!='cli')
  {
  //We send to a browser
  header('Content-Type: audio/mpeg3');
  if(headers_sent())
  $this->error('Some data has already been output to browser, can\'t send mp3 file');
  header('Content-Length: '.strlen($this->str));
  header('Content-Disposition: attachment; filename="'.$path.'"');
  }
  echo $this->str;
  return '';
  }
  }
  ?>

Here’s how I used the class to generate an mp3 file from individual files (in a “sounds” folder) representing each letter. You can, of course, use the above code to concatenate mp3 files for any purpose.

// Specify the word
$petersword = "testword";

$word_count = strlen($petersword);

 // Set up the first file
  if ($word_count > 0) {
  $mp3 = new mp3($cas_fontpath . 'sounds/' . substr($petersword, 0, 1) . '.mp3');
  $mp3->striptags();
  }

// Generate the mp3 file from each letter in the word
  for ($i = 1; $i < $word_count; ++$i) {
  $cas_character = $cas_fontpath . 'sounds/' . substr($petersword, $i, 1);
  $cas_mp3equivalent = new mp3($cas_character . '.mp3');
  $mp3->mergeBehind($cas_mp3equivalent);
  $mp3->striptags();
  }

  // Spit out the audio file!
$mp3->output('word.mp3');

Note: if you need some support using any of the code, I suggest that you visit the original source of the mp3 concatenation code.

This entry was originally posted on Sunday, August 12th, 2007 at 3:47 pm and is filed under PHP, CSS, JavaScript tutorials. You can follow any responses to this entry through the RSS 2.0 feed.