includes/media/GIFMetadataExtractor.php

   1 <?php
   2 /**
   3  * GIF frame counter.
   4  *
   5  * Originally written in Perl by Steve Sanbeg.
   6  * Ported to PHP by Andrew Garrett
   7  * Deliberately not using MWExceptions to avoid external dependencies, encouraging
   8  * redistribution.
   9  *
  10  * @file
  11  * @ingroup Media
  12  */
  13
  14 /**
  15  * GIF frame counter.
  16  *
  17  * @ingroup Media
  18  */
  19 class GIFMetadataExtractor {
  20         static $gif_frame_sep;
  21         static $gif_extension_sep;
  22         static $gif_term;
  23
  24         static function getMetadata( $filename ) {
  25                 self::$gif_frame_sep = pack( "C", ord("," ) );
  26                 self::$gif_extension_sep = pack( "C", ord("!" ) );
  27                 self::$gif_term = pack( "C", ord(";" ) );
  28
  29                 $frameCount = 0;
  30                 $duration = 0.0;
  31                 $isLooped = false;
  32
  33                 if (!$filename)
  34                         throw new Exception( "No file name specified" );
  35                 elseif ( !file_exists($filename) || is_dir($filename) )
  36                         throw new Exception( "File $filename does not exist" );
  37
  38                 $fh = fopen( $filename, 'r' );
  39
  40                 if (!$fh)
  41                         throw new Exception( "Unable to open file $filename" );
  42
  43                 // Check for the GIF header
  44                 $buf = fread( $fh, 6 );
  45                 if ( !($buf == 'GIF87a' || $buf == 'GIF89a') ) {
  46                         throw new Exception( "Not a valid GIF file; header: $buf" );
  47                 }
  48
  49                 // Skip over width and height.
  50                 fread( $fh, 4 );
  51
  52                 // Read BPP
  53                 $buf = fread( $fh, 1 );
  54                 $bpp = self::decodeBPP( $buf );
  55
  56                 // Skip over background and aspect ratio
  57                 fread( $fh, 2 );
  58
  59                 // Skip over the GCT
  60                 self::readGCT( $fh, $bpp );
  61
  62                 while( !feof( $fh ) ) {
  63                         $buf = fread( $fh, 1 );
  64
  65                         if ($buf == self::$gif_frame_sep) {
  66                                 // Found a frame
  67                                 $frameCount++;
  68
  69                                 ## Skip bounding box
  70                                 fread( $fh, 8 );
  71
  72                                 ## Read BPP
  73                                 $buf = fread( $fh, 1 );
  74                                 $bpp = self::decodeBPP( $buf );
  75
  76                                 ## Read GCT
  77                                 self::readGCT( $fh, $bpp );
  78                                 fread( $fh, 1 );
  79                                 self::skipBlock( $fh );
  80                         } elseif ( $buf == self::$gif_extension_sep ) {
  81                                 $buf = fread( $fh, 1 );
  82                                 $extension_code = unpack( 'C', $buf );
  83                                 $extension_code = $extension_code[1];
  84
  85                                 if ($extension_code == 0xF9) {
  86                                         // Graphics Control Extension.
  87                                         fread( $fh, 1 ); // Block size
  88
  89                                         fread( $fh, 1 ); // Transparency, disposal method, user input
  90
  91                                         $buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
  92                                         $delay = unpack( 'v', $buf );
  93                                         $delay = $delay[1];
  94                                         $duration += $delay * 0.01;
  95
  96                                         fread( $fh, 1 ); // Transparent colour index
  97
  98                                         $term = fread( $fh, 1 ); // Should be a terminator
  99                                         $term = unpack( 'C', $term );
 100                                         $term = $term[1];
 101                                         if ($term != 0 )
 102                                                 throw new Exception( "Malformed Graphics Control Extension block" );
 103                                 } elseif ($extension_code == 0xFF) {
 104                                         // Application extension (Netscape info about the animated gif)
 105                                         $blockLength = fread( $fh, 1 );
 106                                         $blockLength = unpack( 'C', $blockLength );
 107                                         $blockLength = $blockLength[1];
 108                                         $data = fread( $fh, $blockLength );
 109
 110                                         // NETSCAPE2.0 (application name)
 111                                         if ($blockLength != 11 || $data != 'NETSCAPE2.0') {
 112                                                 fseek( $fh, -($blockLength + 1), SEEK_CUR );
 113                                                 self::skipBlock( $fh );
 114                                                 continue;
 115                                         }
 116
 117                                         $data = fread( $fh, 2 ); // Block length and introduction, should be 03 01
 118
 119                                         if ($data != "\x03\x01") {
 120                                                 throw new Exception( "Expected \x03\x01, got $data" );
 121                                         }
 122
 123                                         // Unsigned little-endian integer, loop count or zero for "forever"
 124                                         $loopData = fread( $fh, 2 );
 125                                         $loopData = unpack( 'v', $loopData );
 126                                         $loopCount = $loopData[1];
 127
 128                                         if ($loopCount != 1) {
 129                                                 $isLooped = true;
 130                                         }
 131
 132                                         // Read out terminator byte
 133                                         fread( $fh, 1 );
 134                                 } else {
 135                                         self::skipBlock( $fh );
 136                                 }
 137                         } elseif ( $buf == self::$gif_term ) {
 138                                 break;
 139                         } else {
 140                                 $byte = unpack( 'C', $buf );
 141                                 $byte = $byte[1];
 142                                 throw new Exception( "At position: ".ftell($fh). ", Unknown byte ".$byte );
 143                         }
 144                 }
 145
 146                 return array(
 147                         'frameCount' => $frameCount,
 148                         'looped' => $isLooped,
 149                         'duration' => $duration
 150                 );
 151
 152         }
 153
 154         static function readGCT( $fh, $bpp ) {
 155                 if ($bpp > 0) {
 156                         for( $i=1; $i<=pow(2,$bpp); ++$i ) {
 157                                 fread( $fh, 3 );
 158                         }
 159                 }
 160         }
 161
 162         static function decodeBPP( $data ) {
 163                 $buf = unpack( 'C', $data );
 164                 $buf = $buf[1];
 165                 $bpp = ( $buf & 7 ) + 1;
 166                 $buf >>= 7;
 167
 168                 $have_map = $buf & 1;
 169
 170                 return $have_map ? $bpp : 0;
 171         }
 172
 173         static function skipBlock( $fh ) {
 174                 while ( !feof( $fh ) ) {
 175                         $buf = fread( $fh, 1 );
 176                         $block_len = unpack( 'C', $buf );
 177                         $block_len = $block_len[1];
 178                         if ($block_len == 0)
 179                                 return;
 180                         fread( $fh, $block_len );
 181                 }
 182         }
 183
 184 }