how to get frame count?

[khstar2000]

i nedd frame count in render and decorder.
see in following code
$gifStream = new FileStream($target_file);
$gifDecoder = new Decoder($gifStream);
$gifRenderer = new Renderer($gifDecoder);
$gifRenderer->start(function (FrameRenderedEvent $event) {
imagepng($event->renderedFrame, DIR . "/../gif_render/frame{$event->frameIndex}.png");
});
and how to change png filepath and filename(here is gif_render/frame ....png).
then create png, how know png count?

[ghost]

Upd:
This is the best solution, which i have found:

<?php
function FrameCount($File){

if(is_file($File)) $File = file_get_contents($File);
return abs(substr_count($File, "\x21\xf9")-substr_count($File,"\x21\xfe")-2);

}