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( $filename ) {
  16                 self::$gif_frame_sep = pack( "C", ord("," ) );
  17                 self::$gif_extension_sep = pack( "C", ord("!" ) );
  18                 self::$gif_term = pack( "C", ord(";" ) );
  19
  20                 $frameCount = 0;
  21                 $duration = 0.0;
  22                 $isLooped = false;
  23
  24                 if (!$filename)
  25                         throw new Exception( "No file name specified" );
  26                 elseif ( !file_exists($filename) || is_dir($filename) )
  27                         throw new Exception( "File $filename does not exist" );
  28
  29                 $fh = fopen( $filename, 'r' );
  30
  31                 if (!$fh)
  32                         throw new Exception( "Unable to open file $filename" );
  33
  34                 // Check for the GIF header
  35                 $buf = fread( $fh, 6 );
  36                 if ( !($buf == 'GIF87a' || $buf == 'GIF89a') ) {
  37                         throw new Exception( "Not a valid GIF file; header: $buf" );
  38                 }
  39
  40                 // Skip over width and height.
  41                 fread( $fh, 4 );
  42
  43                 // Read BPP
  44                 $buf = fread( $fh, 1 );
  45                 $bpp = self::decodeBPP( $buf );
  46
  47                 // Skip over background and aspect ratio
  48                 fread( $fh, 2 );
  49
  50                 // Skip over the GCT
  51                 self::readGCT( $fh, $bpp );
  52
  53                 while( !feof( $fh ) ) {
  54                         $buf = fread( $fh, 1 );
  55
  56                         if ($buf == self::$gif_frame_sep) {
  57                                 // Found a frame
  58                                 $frameCount++;
  59
  60                                 ## Skip bounding box
  61                                 fread( $fh, 8 );
  62
  63                                 ## Read BPP
  64                                 $buf = fread( $fh, 1 );
  65                                 $bpp = self::decodeBPP( $buf );
  66
  67                                 ## Read GCT
  68                                 self::readGCT( $fh, $bpp );
  69                                 fread( $fh, 1 );
  70                                 self::skipBlock( $fh );
  71                         } elseif ( $buf == self::$gif_extension_sep ) {
  72                                 $buf = fread( $fh, 1 );
  73                                 $extension_code = unpack( 'C', $buf );
  74                                 $extension_code = $extension_code[1];
  75
  76                                 if ($extension_code == 0xF9) {
  77                                         // Graphics Control Extension.
  78                                         fread( $fh, 1 ); // Block size
  79
  80                                         fread( $fh, 1 ); // Transparency, disposal method, user input
  81
  82                                         $buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
  83                                         $delay = unpack( 'v', $buf );
  84                                         $delay = $delay[1];
  85                                         $duration += $delay * 0.01;
  86
  87                                         fread( $fh, 1 ); // Transparent colour index
  88
  89                                         $term = fread( $fh, 1 ); // Should be a terminator
  90                                         $term = unpack( 'C', $term );
  91                                         $term = $term[1];
  92                                         if ($term != 0 )
  93                                                 throw new Exception( "Malformed Graphics Control Extension block" );
  94                                 } elseif ($extension_code == 0xFF) {
  95                                         // Application extension (Netscape info about the animated gif)
  96                                         $blockLength = fread( $fh, 1 );
  97                                         $blockLength = unpack( 'C', $blockLength );
  98                                         $blockLength = $blockLength[1];
  99                                         $data = fread( $fh, $blockLength );
 100
 101                                         // NETSCAPE2.0 (application name)
 102                                         if ($blockLength != 11 || $data != 'NETSCAPE2.0') {
 103                                                 fseek( $fh, -($blockLength + 1), SEEK_CUR );
 104                                                 self::skipBlock( $fh );
 105                                                 continue;
 106                                         }
 107
 108                                         $data = fread( $fh, 2 ); // Block length and introduction, should be 03 01
 109
 110                                         if ($data != "\x03\x01") {
 111                                                 throw new Exception( "Expected \x03\x01, got $data" );
 112                                         }
 113
 114                                         // Unsigned little-endian integer, loop count or zero for "forever"
 115                                         $loopData = fread( $fh, 2 );
 116                                         $loopData = unpack( 'v', $loopData );
 117                                         $loopCount = $loopData[1];
 118
 119                                         if ($loopCount != 1) {
 120                                                 $isLooped = true;
 121                                         }
 122
 123                                         // Read out terminator byte
 124                                         fread( $fh, 1 );
 125                                 } else {
 126                                         self::skipBlock( $fh );
 127                                 }
 128                         } elseif ( $buf == self::$gif_term ) {
 129                                 break;
 130                         } else {
 131                                 $byte = unpack( 'C', $buf );
 132                                 $byte = $byte[1];
 133                                 throw new Exception( "At position: ".ftell($fh). ", Unknown byte ".$byte );
 134                         }
 135                 }
 136
 137                 return array(
 138                         'frameCount' => $frameCount,
 139                         'looped' => $isLooped,
 140                         'duration' => $duration
 141                 );
 142
 143         }
 144
 145         static function readGCT( $fh, $bpp ) {
 146                 if ($bpp > 0) {
 147                         for( $i=1; $i<=pow(2,$bpp); ++$i ) {
 148                                 fread( $fh, 3 );
 149                         }
 150                 }
 151         }
 152
 153         static function decodeBPP( $data ) {
 154                 $buf = unpack( 'C', $data );
 155                 $buf = $buf[1];
 156                 $bpp = ( $buf & 7 ) + 1;
 157                 $buf >>= 7;
 158
 159                 $have_map = $buf & 1;
 160
 161                 return $have_map ? $bpp : 0;
 162         }
 163
 164         static function skipBlock( $fh ) {
 165                 while ( !feof( $fh ) ) {
 166                         $buf = fread( $fh, 1 );
 167                         $block_len = unpack( 'C', $buf );
 168                         $block_len = $block_len[1];
 169                         if ($block_len == 0)
 170                                 return;
 171                         fread( $fh, $block_len );
 172                 }
 173         }
 174
 175 }