includes/media/PNGMetadataExtractor.php

   1 <?php
   2 /**
   3  * PNG frame counter.
   4  * Slightly derived from GIFMetadataExtractor.php
   5  * Deliberately not using MWExceptions to avoid external dependencies, encouraging
   6  * redistribution.
   7  *
   8  * @file
   9  * @ingroup Media
  10  */
  11
  12 /**
  13  * PNG frame counter.
  14  *
  15  * @ingroup Media
  16  */
  17 class PNGMetadataExtractor {
  18         static $png_sig;
  19         static $CRC_size;
  20
  21         static function getMetadata( $filename ) {
  22                 self::$png_sig = pack( "C8", 137, 80, 78, 71, 13, 10, 26, 10 );
  23                 self::$CRC_size = 4;
  24
  25                 $frameCount = 0;
  26                 $loopCount = 1;
  27                 $duration = 0.0;
  28
  29                 if (!$filename)
  30                         throw new Exception( __METHOD__ . ": No file name specified" );
  31                 elseif ( !file_exists($filename) || is_dir($filename) )
  32                         throw new Exception( __METHOD__ . ": File $filename does not exist" );
  33
  34                 $fh = fopen( $filename, 'r' );
  35
  36                 if (!$fh) {
  37                         throw new Exception( __METHOD__ . ": Unable to open file $filename" );
  38                 }
  39
  40                 // Check for the PNG header
  41                 $buf = fread( $fh, 8 );
  42                 if ( $buf != self::$png_sig ) {
  43                         throw new Exception( __METHOD__ . ": Not a valid PNG file; header: $buf" );
  44                 }
  45
  46                 // Read chunks
  47                 while( !feof( $fh ) ) {
  48                         $buf = fread( $fh, 4 );
  49                         if( !$buf ) {
  50                                 throw new Exception( __METHOD__ . ": Read error" );
  51                         }
  52                         $chunk_size = unpack( "N", $buf);
  53                         $chunk_size = $chunk_size[1];
  54
  55                         $chunk_type = fread( $fh, 4 );
  56                         if( !$chunk_type ) {
  57                                 throw new Exception( __METHOD__ . ": Read error" );
  58                         }
  59
  60                         if ( $chunk_type == "acTL" ) {
  61                                 $buf = fread( $fh, $chunk_size );
  62                                 if( !$buf ) {
  63                                         throw new Exception( __METHOD__ . ": Read error" );
  64                                 }
  65
  66                                 $actl = unpack( "Nframes/Nplays", $buf );
  67                                 $frameCount = $actl['frames'];
  68                                 $loopCount = $actl['plays'];
  69                         } elseif ( $chunk_type == "fcTL" ) {
  70                                 $buf = fread( $fh, $chunk_size );
  71                                 if( !$buf ) {
  72                                         throw new Exception( __METHOD__ . ": Read error" );
  73                                 }
  74                                 $buf = substr( $buf, 20 );
  75
  76                                 $fctldur = unpack( "ndelay_num/ndelay_den", $buf );
  77                                 if( $fctldur['delay_den'] == 0 ) $fctldur['delay_den'] = 100;
  78                                 if( $fctldur['delay_num'] ) {
  79                                         $duration += $fctldur['delay_num'] / $fctldur['delay_den'];
  80                                 }
  81                         } elseif ( ( $chunk_type == "IDAT" || $chunk_type == "IEND" ) && $frameCount == 0 ) {
  82                                 // Not a valid animated image. No point in continuing.
  83                                 break;
  84                         } elseif ( $chunk_type == "IEND" ) {
  85                                 break;
  86                         } else {
  87                                 fseek( $fh, $chunk_size, SEEK_CUR );
  88                         }
  89                         fseek( $fh, self::$CRC_size, SEEK_CUR );
  90                 }
  91                 fclose( $fh );
  92
  93                 if( $loopCount > 1 ) {
  94                         $duration *= $loopCount;
  95                 }
  96
  97                 return array(
  98                         'frameCount' => $frameCount,
  99                         'loopCount' => $loopCount,
 100                         'duration' => $duration
 101                 );
 102
 103         }
 104 }