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                 // Check for the PNG header
  40                 $buf = fread( $fh, 8 );
  41                 if ( !($buf == self::$png_sig) ) {
  42                         throw new Exception( __METHOD__ . ": Not a valid PNG file; header: $buf" );
  43                 }
  44
  45                 // Read chunks
  46                 while( !feof( $fh ) ) {
  47                         $buf = fread( $fh, 4 );
  48                         if( !$buf ) {
  49                 throw new Exception( __METHOD__ . ": Read error" );
  50             }
  51                         $chunk_size = unpack( "N", $buf);
  52                         $chunk_size = $chunk_size[1];
  53
  54                         $chunk_type = fread( $fh, 4 );
  55                         if( !$chunk_type ) {
  56                 throw new Exception( __METHOD__ . ": Read error" );
  57             }
  58
  59                         if ( $chunk_type == "acTL" ) {
  60                                 $buf = fread( $fh, $chunk_size );
  61                                 if( !$buf ) {
  62                     throw new Exception( __METHOD__ . ": Read error" );
  63                 }
  64
  65                                 $actl = unpack( "Nframes/Nplays", $buf );
  66                                 $frameCount = $actl['frames'];
  67                                 $loopCount = $actl['plays'];
  68                         } elseif ( $chunk_type == "fcTL" ) {
  69                                 $buf = fread( $fh, $chunk_size );
  70                                 if( !$buf ) {
  71                     throw new Exception( __METHOD__ . ": Read error" );
  72                 }
  73                                 $buf = substr( $buf, 20 );
  74
  75                                 $fctldur = unpack( "ndelay_num/ndelay_den", $buf );
  76                                 if( $fctldur['delay_den'] == 0 ) $fctldur['delay_den'] = 100;
  77                                 if( $fctldur['delay_num'] ) {
  78                                         $duration += $fctldur['delay_num'] / $fctldur['delay_den'];
  79                                 }
  80                         } elseif ( ( $chunk_type == "IDAT" || $chunk_type == "IEND" ) && $frameCount == 0 ) {
  81                                 // Not a valid animated image. No point in continuing.
  82                                 break;
  83                         } elseif ( $chunk_type == "IEND" ) {
  84                                 break;
  85                         } else {
  86                                 fseek( $fh, $chunk_size, SEEK_CUR );
  87                         }
  88                         fseek( $fh, self::$CRC_size, SEEK_CUR );
  89                 }
  90                 fclose( $fh );
  91
  92                 if( $loopCount > 1 ) {
  93                         $duration *= $loopCount;
  94                 }
  95
  96                 return array(
  97                         'frameCount' => $frameCount,
  98                         'loopCount' => $loopCount,
  99                         'duration' => $duration
 100                 );
 101
 102         }
 103 }