lots of improvements:

hover animation
correct jumpback position after video view
load when scroll - not all at beginning

php/extractvideopreviews.php

@@ -2,5 +2,5 @@
 $arr = scandir("../videos/prn/");
 
 foreach ($arr as $elem) {
-  shell_exec("ffmpeg -ss 00:04:00 -i \"../videos/prn/$elem\" -vframes 1 -q:v 2 \"$elem.jpg\"");
+    shell_exec("ffmpeg -ss 00:04:00 -i \"../videos/prn/$elem\" -vframes 1 -q:v 2 \"$elem.jpg\"");
 }