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|
<?php
/**
* GIF frame counter.
* Originally written in Perl by Steve Sanbeg.
* Ported to PHP by Andrew Garrett
* Deliberately not using MWExceptions to avoid external dependencies, encouraging
* redistribution.
*/
class GIFMetadataExtractor {
static $gif_frame_sep;
static $gif_extension_sep;
static $gif_term;
static function getMetadata( $filename ) {
self::$gif_frame_sep = pack( "C", ord("," ) );
self::$gif_extension_sep = pack( "C", ord("!" ) );
self::$gif_term = pack( "C", ord(";" ) );
$frameCount = 0;
$duration = 0.0;
$isLooped = false;
if (!$filename)
throw new Exception( "No file name specified" );
elseif ( !file_exists($filename) || is_dir($filename) )
throw new Exception( "File $filename does not exist" );
$fh = fopen( $filename, 'r' );
if (!$fh)
throw new Exception( "Unable to open file $filename" );
// Check for the GIF header
$buf = fread( $fh, 6 );
if ( !($buf == 'GIF87a' || $buf == 'GIF89a') ) {
throw new Exception( "Not a valid GIF file; header: $buf" );
}
// Skip over width and height.
fread( $fh, 4 );
// Read BPP
$buf = fread( $fh, 1 );
$bpp = self::decodeBPP( $buf );
// Skip over background and aspect ratio
fread( $fh, 2 );
// Skip over the GCT
self::readGCT( $fh, $bpp );
while( !feof( $fh ) ) {
$buf = fread( $fh, 1 );
if ($buf == self::$gif_frame_sep) {
// Found a frame
$frameCount++;
## Skip bounding box
fread( $fh, 8 );
## Read BPP
$buf = fread( $fh, 1 );
$bpp = self::decodeBPP( $buf );
## Read GCT
self::readGCT( $fh, $bpp );
fread( $fh, 1 );
self::skipBlock( $fh );
} elseif ( $buf == self::$gif_extension_sep ) {
$buf = fread( $fh, 1 );
$extension_code = unpack( 'C', $buf );
$extension_code = $extension_code[1];
if ($extension_code == 0xF9) {
// Graphics Control Extension.
fread( $fh, 1 ); // Block size
fread( $fh, 1 ); // Transparency, disposal method, user input
$buf = fread( $fh, 2 ); // Delay, in hundredths of seconds.
$delay = unpack( 'v', $buf );
$delay = $delay[1];
$duration += $delay * 0.01;
fread( $fh, 1 ); // Transparent colour index
$term = fread( $fh, 1 ); // Should be a terminator
$term = unpack( 'C', $term );
$term = $term[1];
if ($term != 0 )
throw new Exception( "Malformed Graphics Control Extension block" );
} elseif ($extension_code == 0xFF) {
// Application extension (Netscape info about the animated gif)
$blockLength = fread( $fh, 1 );
$blockLength = unpack( 'C', $blockLength );
$blockLength = $blockLength[1];
$data = fread( $fh, $blockLength );
// NETSCAPE2.0 (application name)
if ($blockLength != 11 || $data != 'NETSCAPE2.0') {
fseek( $fh, -($blockLength + 1), SEEK_CUR );
self::skipBlock( $fh );
continue;
}
$data = fread( $fh, 2 ); // Block length and introduction, should be 03 01
if ($data != "\x03\x01") {
throw new Exception( "Expected \x03\x01, got $data" );
}
// Unsigned little-endian integer, loop count or zero for "forever"
$loopData = fread( $fh, 2 );
$loopData = unpack( 'v', $loopData );
$loopCount = $loopData[1];
if ($loopCount != 1) {
$isLooped = true;
}
// Read out terminator byte
fread( $fh, 1 );
} else {
self::skipBlock( $fh );
}
} elseif ( $buf == self::$gif_term ) {
break;
} else {
$byte = unpack( 'C', $buf );
$byte = $byte[1];
throw new Exception( "At position: ".ftell($fh). ", Unknown byte ".$byte );
}
}
return array(
'frameCount' => $frameCount,
'looped' => $isLooped,
'duration' => $duration
);
}
static function readGCT( $fh, $bpp ) {
if ($bpp > 0) {
for( $i=1; $i<=pow(2,$bpp); ++$i ) {
fread( $fh, 3 );
}
}
}
static function decodeBPP( $data ) {
$buf = unpack( 'C', $data );
$buf = $buf[1];
$bpp = ( $buf & 7 ) + 1;
$buf >>= 7;
$have_map = $buf & 1;
return $have_map ? $bpp : 0;
}
static function skipBlock( $fh ) {
while ( !feof( $fh ) ) {
$buf = fread( $fh, 1 );
$block_len = unpack( 'C', $buf );
$block_len = $block_len[1];
if ($block_len == 0)
return;
fread( $fh, $block_len );
}
}
}
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