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
  39                 $fh = fopen( $filename, 'r' );
  40
  41                 if ( !$fh ) {
  42                         throw new Exception( "Unable to open file $filename" );
  43                 }
  44
  45                 // Check for the GIF header
  46                 $buf = fread( $fh, 6 );
  47                 if ( !($buf == 'GIF87a' || $buf == 'GIF89a') ) {
  48                         throw new Exception( "Not a valid GIF file; header: $buf" );
  49                 }
  50
  51                 // Skip over width and height.
  52                 fread( $fh, 4 );
  53
  54                 // Read BPP
  55                 $buf = fread( $fh, 1 );
  56                 $bpp = self::decodeBPP( $buf );
  57
  58                 // Skip over background and aspect ratio
  59                 fread( $fh, 2 );
  60
  61                 // Skip over the GCT
  62                 self::readGCT( $fh, $bpp );
  63
  64                 while( !feof( $fh ) ) {
  65                         $buf = fread( $fh, 1 );
  66
  67                         if ($buf == self::$gif_frame_sep) {
  68                                 // Found a frame
  69                                 $frameCount++;
  70
  71                                 ## Skip bounding box
  72                                 fread( $fh, 8 );
  73
  74                                 ## Read BPP
  75                                 $buf = fread( $fh, 1 );
  76                                 $bpp = self::decodeBPP( $buf );
  77
  78                                 ## Read GCT
  79                                 self::readGCT( $fh, $bpp );
  80                                 fread( $fh, 1 );
  81                                 self::skipBlock( $fh );
  82                         } elseif ( $buf == self::$gif_extension_sep ) {
  83                                 $buf = fread( $fh, 1 );
  84                                 $extension_code = unpack( 'C', $buf );
  85                                 $extension_code = $extension_code[1];
  86
  87                                 if ($extension_code == 0xF9) {
  88                                         // Graphics Control Extension.
  89                                         fread( $fh, 1 ); // Block size
  90
  91                                         fread( $fh, 1 ); // Transparency, disposal method, user input
  92
  93                                         $buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
  94                                         $delay = unpack( 'v', $buf );
  95                                         $delay = $delay[1];
  96                                         $duration += $delay * 0.01;
  97
  98                                         fread( $fh, 1 ); // Transparent colour index
  99
 100                                         $term = fread( $fh, 1 ); // Should be a terminator
 101                                         $term = unpack( 'C', $term );
 102                                         $term = $term[1];
 103                                         if ($term != 0 ) {
 104                                                 throw new Exception( "Malformed Graphics Control Extension block" );
 105                                         }
 106                                 } elseif ($extension_code == 0xFF) {
 107                                         // Application extension (Netscape info about the animated gif)
 108                                         $blockLength = fread( $fh, 1 );
 109                                         $blockLength = unpack( 'C', $blockLength );
 110                                         $blockLength = $blockLength[1];
 111                                         $data = fread( $fh, $blockLength );
 112
 113                                         // NETSCAPE2.0 (application name)
 114                                         if ($blockLength != 11 || $data != 'NETSCAPE2.0') {
 115                                                 fseek( $fh, -($blockLength + 1), SEEK_CUR );
 116                                                 self::skipBlock( $fh );
 117                                                 continue;
 118                                         }
 119
 120                                         $data = fread( $fh, 2 ); // Block length and introduction, should be 03 01
 121
 122                                         if ($data != "\x03\x01") {
 123                                                 throw new Exception( "Expected \x03\x01, got $data" );
 124                                         }
 125
 126                                         // Unsigned little-endian integer, loop count or zero for "forever"
 127                                         $loopData = fread( $fh, 2 );
 128                                         $loopData = unpack( 'v', $loopData );
 129                                         $loopCount = $loopData[1];
 130
 131                                         if ($loopCount != 1) {
 132                                                 $isLooped = true;
 133                                         }
 134
 135                                         // Read out terminator byte
 136                                         fread( $fh, 1 );
 137                                 } else {
 138                                         self::skipBlock( $fh );
 139                                 }
 140                         } elseif ( $buf == self::$gif_term ) {
 141                                 break;
 142                         } else {
 143                                 $byte = unpack( 'C', $buf );
 144                                 $byte = $byte[1];
 145                                 throw new Exception( "At position: ".ftell($fh). ", Unknown byte ".$byte );
 146                         }
 147                 }
 148
 149                 return array(
 150                         'frameCount' => $frameCount,
 151                         'looped' => $isLooped,
 152                         'duration' => $duration
 153                 );
 154         }
 155
 156         static function readGCT( $fh, $bpp ) {
 157                 if ( $bpp > 0 ) {
 158                         for( $i=1; $i<=pow( 2, $bpp ); ++$i ) {
 159                                 fread( $fh, 3 );
 160                         }
 161                 }
 162         }
 163
 164         static function decodeBPP( $data ) {
 165                 $buf = unpack( 'C', $data );
 166                 $buf = $buf[1];
 167                 $bpp = ( $buf & 7 ) + 1;
 168                 $buf >>= 7;
 169
 170                 $have_map = $buf & 1;
 171
 172                 return $have_map ? $bpp : 0;
 173         }
 174
 175         static function skipBlock( $fh ) {
 176                 while ( !feof( $fh ) ) {
 177                         $buf = fread( $fh, 1 );
 178                         $block_len = unpack( 'C', $buf );
 179                         $block_len = $block_len[1];
 180                         if ($block_len == 0) {
 181                                 return;
 182                         }
 183                         fread( $fh, $block_len );
 184                 }
 185         }
 186 }