If it's not possible to do that, you may have to save the video first. There are various browser extensions for that. here is one.
https://chromewebstore.google.com/detail/video-downloader-cococut/ekhbcipncbkfpkaianbjbcbmfehjflpf(http://www.autoadmit.com/thread.php?thread_id=5528056&forum_id=2#47657752)