[is animated GIF] Detect if a GIF file is animated or not #php #function #gif

isAnimatedGIF.php

<?php

/* ----------------------------------------------------------------------------- */
/* [is animated GIF] Detect if a GIF file is animated or not #php #function #gif */
/* ----------------------------------------------------------------------------- */

/**
 * Detect if a GIF file is animated or not
 * 
 * We read through the file til we reach the end of the file, or we've found at least 2 frame headers
 * an animated gif contains multiple "frames", with each frame having a header made up of:
 * a static 4-byte sequence (\x00\x21\xF9\x04)
 * 4 variable bytes
 * a static 2-byte sequence (\x00\x2C) (some variants may use \x00\x21 ?)
 * @see https://php.net/manual/en/function.imagecreatefromgif.php#104473
 */

function isAnimatedGIF($gif) {
    if ( !($fh=@fopen($gif, 'rb'))) return false;
    $count = 0;    
    while ( !feof($fh) and $count < 2 ) {
        $chunk = fread($fh, 1024 * 100); // read 100kb at a time
        $count += preg_match_all('#\x00\x21\xF9\x04.{4}\x00(\x2C|\x21)#s', $chunk, $matches);
    }
    fclose($fh);
    return $count > 1;
}

echo 'GIF but not animated ' . isAnimatedGIF('error.gif') . ' &nbsp; &nbsp; ""=false<br><br>';
echo 'This GIF is animated ' . isAnimatedGIF('https://talks.php.net/presentations/slides/intro/test.gif').' "1"=true';