View file modules/viewer/video.php

<?php
require_once $_SERVER['DOCUMENT_ROOT'].'/system/function.php';
header('Content-type: image/jpeg');

$name = isset($_GET['file']) ? guard($_GET['file']) : null;
$url = H.'/files/'.$name;
$frame = 13;
$tmpPath = H."/files/tmp/".$name.".jpeg";

if (empty($name)) {
	header('HTTP/2.0 404 Not found');
	exit;
} elseif (!file_exists($url)) {
	header('HTTP/2.0 404 Not found');
	exit;
}

$video = new ffmpeg_movie($url);
$image = $video->getFrame($frame);
$thumbnail = $image->toGDImage();

if (!file_exists($tmpPath)) {
    imagejpeg($thumbnail, $tmpPath);
    imagejpeg($thumbnail);
    imagedestroy($thumbnail);
    exit;
} else {
    $img = file_get_contents($tmpPath);
    echo $img;
    exit;
}

?>