You should never access the renditions directly. Please find below example on geometrixx [1] how to get url for original file and rendition. In case you are not using dimension in rendition then need to customize thumbnail servlet
Verify your component and make sure to use servlet to pick the renditon. The example i gave for image but holds good for video also.
[1]
http://<host>:<port>/content/dam/geometrixx/banners/techsummit.jpg
http://<host>:<port>/content/dam/geometrixx/banners/techsummit.jpg.thumb.319.319.png