I hate created an improved version of frank at huddler dot com's is_ani function, which keeps score even between hunks. Hope this helps!
/**
* Check if the provided file is an animated gif.
*
* @param string $fileName
* @return bool
*/
function isAnimatedGif($fileName)
{
$fh = fopen($fileName, 'rb');
if (!$fh) {
return false;
}
$totalCount = 0;
$chunk = '';
// An animated gif contains multiple "frames", with each frame having a header made up of:
// * a static 4-byte sequence (\x00\x21\xF9\x04)
// * 4 variable bytes
// * a static 2-byte sequence (\x00\x2C) (some variants may use \x00\x21 ?)
// We read through the file until we reach the end of it, or we've found at least 2 frame headers.
while (!feof($fh) && $totalCount < 2) {
// Read 100kb at a time and append it to the remaining chunk.
$chunk .= fread($fh, 1024 * 100);
$count = preg_match_all('#\x00\x21\xF9\x04.{4}\x00(\x2C|\x21)#s', $chunk, $matches);
$totalCount += $count;
// Execute this block only if we found at least one match,
// and if we did not reach the maximum number of matches needed.
if ($count > 0 && $totalCount < 2) {
// Get the last full expression match.
$lastMatch = end($matches[0]);
// Get the string after the last match.
$end = strrpos($chunk, $lastMatch) + strlen($lastMatch);
$chunk = substr($chunk, $end);
}
}
fclose($fh);
return $totalCount > 1;
}
