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SWF Frame Rate Extraction

An article by ERT Mentor VGR

1. Purpose

To extract ***from PHP*** various SWF file information, in particular the difficult-to-obtain "Frame Rate":

2. Introduction

The first idea is of course not to reinvent the wheel and search for an already-made solution:

3. Third-party Tools

The tools I found and tried are usually:

• Video Converters (SWF to AVI, etc) like Magic Swf2Avi 3.11.
• SWF Decompilers, Decompressors or pure Extractors, like Action Script Viewer or SWF Decompiler or SWF Extractor Free or WinSWF Extractor, when you transform a SWF file in its collection of Resources in binary format.
• SWF Editors, like SWF Editor or Flash Digger, when you perform manually some operations on SWF files.

The conclusion of this tools analysis is that I found them:

• Sometimes clumsy
• Usually too low-level (hexadecimal dump) or too bloated (Windows executable with GUI) to be really useable from PHP
• Lacking a command-line mode (so that they could be called from PHP via exec() for instance) or to get output on the console (stdout)
• Always platform-dependent, which is incompatible with my use of PHP scripts
• Giving out too much or too few information
• And moreover, NOT displaying efficiently the Frame Rate (in fps, frames per second)

So I had to find a really good way to extract information from a SWF file. I had two trivial ways to go : (a) find an already-made SWF Header Extractor, or (b) work at the binary level.

At first, of course, I turned to the PHP documentation (http://www.php.net/manual/en/) and found out the LibSWF and Ming libraries as candidates.

4. PHP common libraries - LibSWF

PHP has since long (PHP 4 RC2) "Shockwave Flash Functions" (see http://www.php.net/manual/en/ref.swf.php)
The two problems are that (a) it is not available on Windows, and I don't want to use a custom port or emulator (Cygwin...), (b) it can only CREATE SWF files. There is no GetFrameRate() function and no Getter at all.

5. PHP common libraries - Ming

Ming is now a standard library and was added in PHP 4.0.5. See http://www.php.net/manual/en/ref.ming.php.
The "only" problem is that the necessary SWFVideoStream object is only available in the CVS version of the current PHP ;-)

PHP code:

$video= new SWFVideoStream ($_GET['file']);
echo "number of frames is ".$video->getNumFrames().'<br>';

Results:

Fatal error: Cannot instantiate non-existent 
class: swfvideostream in FlashGetFrameRate.php on line 15

6. My Solution

I finally found out the solution I wanted : a ready-made binary-level analyzer written in PHP. All we're left to is write a correct instantiation of the new class and use the defined methods to get the frame rate. Or I could have extended the class to add a GetFrameRate() getter.

The Library Header:

This a well-written little-known PHP class of 6877 bytes and which deserves better visibility on the Web, even if it is known since 2004 ;-)
You can already find it at :

• Main Repository : http://slainte.phpclasses.org/swfheader [linked page is blank at the time I write]
• Main Author's Site : http://www.bisinteractive.net/ [link is broken at the time I write]
• http://www.zend.com/codex.php?id=1382&single=1
• http://phpclasses.linuxpourtous.com/browse/package/1653.html
• Local Copy on this Server : swfheader.class.txt For this file and all the .php files referenced here, you will need to change the file extension from .txt to .php before using them.

<?php
//---------------------------------------------------
// SWF HEADER - version 1.0
// Small utility class to determine basic data from a 
// SWF file header Does not need any php-flash extension, 
// based on raw binary data reading
//----------------------------------------------------
//   SWFHEADER CLASS - PHP SWF header parser
//   Copyright (C) 2004  Carlos Falo Hervás
//   This library is free software; you can redistribute 
//   it and/or modify it under the terms of the GNU Lesser 
//   General Public License as published by the Free 
//   Software Foundation; either version 2.1 of the License, 
//   or (at your option) any later version.
//-----------------------------------------------------

class swfheader {
  var $debug ;          // Output DEBUG info
  var $fname ;          // SWF file analyzed
  var $magic ;          // Magic in a SWF file (FWS or CWS)
  var $compressed ;     // Flag to indicate a compressed file (CWS)
  var $version ;        // Flash version
  var $size ;           // Uncompressed file size (in bytes)
  var $width ;          // Flash movie native width
  var $height ;         // Flash movie native height
  var $valid ;          // Valid SWF file
  var $fps ;            // Flash movie native frame-rate
  var $frames ;         // Flash movie total frames
  //----------------------------------------------------    
  // swfheader($debug) :    Constructor, basically does 
  //                        nothing but initilize
  //                        debug and data fields
  //----------------------------------------------------
  function swfheader($debug = false) {}
  //----------------------------------------------------    
  // init() : initialize the data fields to "empty" values
  //----------------------------------------------------
  function init() {}
  //----------------------------------------------------
  // loadswf($filename) : loads $filename and stores data 
  // from it's header
  //----------------------------------------------------
  function getDimensions($filename) {} 
  // returns String ; object has been updated
}
?>

My PHP code:

Local Copy on this Server : FlashGetFrameRate.txt

<?php
//
// FlashGetFrameRate.php : analyze of a Flash (SWF) file
//
//VGR09062006 Creation with Ming to get the fps of an SWF "video"
//
// TODO : Nil
//

if (!isset($_GET['file'])) { 
   die("Please feed me a filename in 'file' parameter"); 
   exit; }

if (strlen(trim($_GET['file']))==0) die("Empty filename");
else if (!file_exists($_GET['file'])) 
     die("Could not open file '{$_GET['file']}'");
else { // let's go
  //$video= new SWFVideoStream ($_GET['file']); 
  // type : SWFVideoStream (VGR REM : unavailable, CVS only)
  //echo "number of frames is ".$video->getNumFrames().'<br>';
  require('swfheader.class.php');
  $video=new swfheader();
  $thedim=str_replace('|','x',$video->getDimensions($_GET['file']));
echo "AnalFlasp.php v 1.0 ©2006 VGR for ";
echo "Edaìn Works Ltd - uses swfheader class ";
echo "© 2004 Carlos Falo Hervás<hr>file {$_GET['file']} <br>";
echo "dimensions $thedim px<br><pre>";
  print_r($video);
  echo '</pre>';
}
?>

You may see it in action at http://www.fecj.org/extra/AnalFlash/FlashGetFrameRate.php and one file available locally is monster_NL.swf.

Result:

FlashGetFrameRate.php v 1.0 ©2006 
VGR for 

Edaìn Works Ltd - 
uses swfheader class © 2004 Carlos Falo Hervás
file monster_NL.swf
dimensions 425x600 px

swfheader Object
(
    [debug] => 
    [fname] => monster_NL.swf
    [magic] => CWS
    [compressed] => 1
    [version] => 6
    [size] => 46871
    [width] => 425
    [height] => 600
    [valid] => 1
    [fps] => Array
        (
            [0] => 0
            [1] => 18
        )

    [frames] => 1
)

And the Frame Rate is ... 18 fps. CQFD.

8. Extending the technique

You can extract any kind of header field using the same script and looking at the print_r() results.

9. Conclusion

This technique is extremely simple and efficient and does the job well.
Many many thanks to the Author of the Library : Carlos Falo Hervás (SP)

© Copyright VGR 2006-2007

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