includes/media/GIFMetadataExtractor.php

   1 <?php
   2 /**
   3   * GIF frame counter.
   4   * Originally written in Perl by Steve Sanbeg.
   5   * Ported to PHP by Andrew Garrett
   6   * Deliberately not using MWExceptions to avoid external dependencies, encouraging
   7   * redistribution.
   8   */
   9
  10 class GIFMetadataExtractor {
  11         static $gif_frame_sep;
  12         static $gif_extension_sep;
  13         static $gif_term;
  14
  15         static function getMetadata( $filename ) {
  16                 wfProfileIn( __METHOD__ );
  17
  18                 self::$gif_frame_sep = pack( "C", ord("," ) );
  19                 self::$gif_extension_sep = pack( "C", ord("!" ) );
  20                 self::$gif_term = pack( "C", ord(";" ) );
  21
  22                 $frameCount = 0;
  23                 $duration = 0.0;
  24                 $isLooped = false;
  25
  26                 if (!$filename)
  27                         throw new Exception( "No file name specified" );
  28                 elseif ( !file_exists($filename) || is_dir($filename) )
  29                         throw new Exception( "File $filename does not exist" );
  30
  31                 $fh = fopen( $filename, 'r' );
  32
  33                 if (!$fh)
  34                         throw new Exception( "Unable to open file $filename" );
  35
  36                 // Check for the GIF header
  37                 $buf = fread( $fh, 6 );
  38                 if ( !($buf == 'GIF87a' || $buf == 'GIF89a') ) {
  39                         throw new Exception( "Not a valid GIF file; header: $buf" );
  40                 }
  41
  42                 // Skip over width and height.
  43                 fread( $fh, 4 );
  44
  45                 // Read BPP
  46                 $buf = fread( $fh, 1 );
  47                 $bpp = self::decodeBPP( $buf );
  48
  49                 // Skip over background and aspect ratio
  50                 fread( $fh, 2 );
  51
  52                 // Skip over the GCT
  53                 self::readGCT( $fh, $bpp );
  54
  55                 while( !feof( $fh ) ) {
  56                         $buf = fread( $fh, 1 );
  57
  58                         if ($buf == self::$gif_frame_sep) {
  59                                 // Found a frame
  60                                 $frameCount++;
  61
  62                                 ## Skip dimensions (Why is this 8 bytes and not 4?)
  63                                 fread( $fh, 8 );
  64
  65                                 ## Read BPP
  66                                 $buf = fread( $fh, 1 );
  67                                 $bpp = self::decodeBPP( $buf );
  68
  69                                 ## Read GCT
  70                                 self::readGCT( $fh, $bpp );
  71                                 fread( $fh, 1 );
  72                                 self::skipBlock( $fh );
  73                         } elseif ( $buf == self::$gif_extension_sep ) {
  74                                 $buf = fread( $fh, 1 );
  75                                 $extension_code = unpack( 'C', $buf );
  76                                 $extension_code = $extension_code[1];
  77
  78                                 if ($extension_code == 0xF9) {
  79                                         // Graphics Control Extension.
  80                                         fread( $fh, 1 ); // Block size
  81                                         fread( $fh, 1 ); // Transparency, disposal method, user input
  82
  83                                         $buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
  84                                         $delay = unpack( 'v', $buf );
  85                                         $delay = $delay[1];
  86                                         $duration += $delay * 0.01;
  87
  88                                         fread( $fh, 1 ); // Transparent colour index
  89
  90                                         $term = fread( $fh, 1 ); // Should be a terminator
  91                                         $term = unpack( 'C', $term );
  92                                         $term = $term[1];
  93                                         if ($term != 0 )
  94                                                 throw new Exception( "Malformed Graphics Control Extension block" );
  95                                 } elseif ($extension_code == 0xFF) {
  96                                         // Application extension (Netscape info about the animated gif)
  97                                         $blockLength = fread( $fh, 1 );
  98                                         $blockLength = unpack( 'C', $blockLength );
  99                                         $blockLength = $blockLength[1];
 100                                         $data = fread( $fh, $blockLength );
 101
 102                                         // NETSCAPE2.0 (application name)
 103                                         if ($blockLength != 11 || $data != 'NETSCAPE2.0') {
 104                                                 self::skipBlock();
 105                                                 continue;
 106                                         }
 107
 108                                         fread( $fh, 2 ); // Block length and introduction, should be 03 01
 109
 110                                         // Unsigned little-endian integer, loop count or zero for "forever"
 111                                         $loopData = fread( $fh, 2 );
 112                                         $loopData = unpack( 'v', $loopData );
 113                                         $loopCount = $loopData[1];
 114
 115                                         if ($loopCount != 1) {
 116                                                 $isLooped = true;
 117                                         }
 118
 119                                         // Read out terminator byte
 120                                         fread( $fh, 1 );
 121                                 }
 122                         } elseif ( $buf == self::$gif_term ) {
 123                                 break;
 124                         } else {
 125                                 $byte = unpack( 'C', $buf );
 126                                 $byte = $byte[1];
 127                                 throw new Exception( "At position: ".ftell($fh). ", Unknown byte ".$byte );
 128                         }
 129                 }
 130
 131                 wfProfileOut( __METHOD__ );
 132
 133                 return array(
 134                         'frameCount' => $frameCount,
 135                         'looped' => $isLooped,
 136                         'duration' => $duration
 137                 );
 138
 139         }
 140
 141         static function readGCT( $fh, $bpp ) {
 142                 if ($bpp > 0) {
 143                         for( $i=1; $i<=pow(2,$bpp); ++$i ) {
 144                                 fread( $fh, 3 );
 145                         }
 146                 }
 147         }
 148
 149         static function decodeBPP( $data ) {
 150                 $buf = unpack( 'C', $data );
 151                 $buf = $buf[1];
 152                 $bpp = ( $buf & 7 ) + 1;
 153                 $buf >>= 7;
 154
 155                 $have_map = $buf & 1;
 156
 157                 return $have_map ? $bpp : 0;
 158         }
 159
 160         static function skipBlock( $fh ) {
 161                 while ( !feof( $fh ) ) {
 162                         $buf = fread( $fh, 1 );
 163                         $block_len = unpack( 'C', $buf );
 164                         $block_len = $block_len[1];
 165                         if ($block_len == 0)
 166                                 return;
 167                         fread( $fh, $block_len );
 168                 }
 169         }
 170
 171 }