Change allowed file extensions per attribute

Observer.php

<?php
public function changeAllowedFileExtensions(Varien_Event_Observer $observer) {
    $file = $observer->getEvent()->getFile();
    
    // Assuming 'document' and 'sample_video' are your attribute codes
    if ($file->getName() == 'document') {
        $file->setData('allowed_extensions', array('pdf'));
    } else if ($file->getName() == 'sample_video') {
        $file->setData('allowed_extensions', array('mp4', 'mpeg', 'avi'));
    }
    
    return $this;
}