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