This problem occurs with Opera (chrome based) but not in Firefox or Chrome.
The mp4 posts are shown with the wrong html tag, as if it were image files
ex. post #2153741
<img alt="f1f474bbe49e625a0d986818e1251fdd" data-fav-count="4" data-flags="" data-has-active-children="false" data-has-children="false" data-large-height="480" data-large-width="600" data-original-height="480" data-original-width="600" data-rating="s" data-score="5" data-tags="2girls akemi_homura animated bow detached_sleeves hair_bow hairband magical_girl mahou_shoujo_madoka_magica mp4 multiple_girls oda_takayuki ponytail rope sakura_kyouko simple_background white_background" data-pools="pool:6812 pool:series" data-uploader="john1980" height="480" width="600" id="image" src="/data/f1f474bbe49e625a0d986818e1251fdd.mp4">
Inspected the section and change manually to
<video id="image" autoplay="autoplay" loop="loop" controls="controls" src="/data/f1f474bbe49e625a0d986818e1251fdd.mp4" height="480" width="600"></video>
Work perfectly.