Here’s a simple solution:
<?php
$images = get_field('gallery');
foreach( $images as $image ):
$data_type = pathinfo($image['url'], PATHINFO_EXTENSION);
if ($data_type == 'mp4') {?>
<video>
<source src="<?php echo $image['url'];?>" type="video/mp4">
Your browser does not support the video tag.
</video>
<?php } else {
echo wp_get_attachment_image($image['ID'], 'large');
} endforeach;
?>