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                 $bitDepth = 0;
  29                 $colorType = 'unknown';
  30
  31                 if (!$filename)
  32                         throw new Exception( __METHOD__ . ": No file name specified" );
  33                 elseif ( !file_exists($filename) || is_dir($filename) )
  34                         throw new Exception( __METHOD__ . ": File $filename does not exist" );
  35
  36                 $fh = fopen( $filename, 'r' );
  37
  38                 if (!$fh) {
  39                         throw new Exception( __METHOD__ . ": Unable to open file $filename" );
  40                 }
  41
  42                 // Check for the PNG header
  43                 $buf = fread( $fh, 8 );
  44                 if ( $buf != self::$png_sig ) {
  45                         throw new Exception( __METHOD__ . ": Not a valid PNG file; header: $buf" );
  46                 }
  47
  48                 // Read chunks
  49                 while( !feof( $fh ) ) {
  50                         $buf = fread( $fh, 4 );
  51                         if( !$buf ) {
  52                                 throw new Exception( __METHOD__ . ": Read error" );
  53                         }
  54                         $chunk_size = unpack( "N", $buf);
  55                         $chunk_size = $chunk_size[1];
  56
  57                         $chunk_type = fread( $fh, 4 );
  58                         if( !$chunk_type ) {
  59                                 throw new Exception( __METHOD__ . ": Read error" );
  60                         }
  61
  62                         if ( $chunk_type == "IHDR" ) {
  63                                 $buf = fread( $fh, $chunk_size );
  64                                 if( !$buf ) {
  65                                         throw new Exception( __METHOD__ . ": Read error" );
  66                                 }
  67                                 $bitDepth = ord( substr( $buf, 8, 1 ) );
  68                                 // Detect the color type in British English as per the spec
  69                                 // http://www.w3.org/TR/PNG/#11IHDR
  70                                 switch ( ord( substr( $buf, 9, 1 ) ) ) {
  71                                         case 0:
  72                                                 $colorType = 'greyscale';
  73                                                 break;
  74                                         case 2:
  75                                                 $colorType = 'truecolour';
  76                                                 break;
  77                                         case 3:
  78                                                 $colorType = 'index-coloured';
  79                                                 break;
  80                                         case 4:
  81                                                 $colorType = 'greyscale-alpha';
  82                                                 break;
  83                                         case 6:
  84                                                 $colorType = 'truecolour-alpha';
  85                                                 break;
  86                                         default:
  87                                                 $colorType = 'unknown';
  88                                                 break;
  89                                 }
  90                         } elseif ( $chunk_type == "acTL" ) {
  91                                 $buf = fread( $fh, $chunk_size );
  92                                 if( !$buf ) {
  93                                         throw new Exception( __METHOD__ . ": Read error" );
  94                                 }
  95
  96                                 $actl = unpack( "Nframes/Nplays", $buf );
  97                                 $frameCount = $actl['frames'];
  98                                 $loopCount = $actl['plays'];
  99                         } elseif ( $chunk_type == "fcTL" ) {
 100                                 $buf = fread( $fh, $chunk_size );
 101                                 if( !$buf ) {
 102                                         throw new Exception( __METHOD__ . ": Read error" );
 103                                 }
 104                                 $buf = substr( $buf, 20 );
 105
 106                                 $fctldur = unpack( "ndelay_num/ndelay_den", $buf );
 107                                 if( $fctldur['delay_den'] == 0 ) $fctldur['delay_den'] = 100;
 108                                 if( $fctldur['delay_num'] ) {
 109                                         $duration += $fctldur['delay_num'] / $fctldur['delay_den'];
 110                                 }
 111                         } elseif ( ( $chunk_type == "IDAT" || $chunk_type == "IEND" ) && $frameCount == 0 ) {
 112                                 // Not a valid animated image. No point in continuing.
 113                                 break;
 114                         } elseif ( $chunk_type == "IEND" ) {
 115                                 break;
 116                         } else {
 117                                 fseek( $fh, $chunk_size, SEEK_CUR );
 118                         }
 119                         fseek( $fh, self::$CRC_size, SEEK_CUR );
 120                 }
 121                 fclose( $fh );
 122
 123                 if( $loopCount > 1 ) {
 124                         $duration *= $loopCount;
 125                 }
 126
 127                 return array(
 128                         'frameCount' => $frameCount,
 129                         'loopCount' => $loopCount,
 130                         'duration' => $duration,
 131                         'bitDepth' => $bitDepth,
 132                         'colorType' => $colorType,
 133                 );
 134
 135         }
 136 }