It looks like you are using a slider plugin for this?
I see the following code, which looks good to me, but maybe the JS with your slider plugin isn’t working well:
<div class="mobile-video-image" style="background-image: url(http://web.stanford.edu/group/surf2/cgi-bin/w/wp-content/uploads/2017/05/golden-wave.jpg)"> <span class="ie-fix"></span> </div><div class="video-wrap"><video class="slider-video" width="1800" height="700" preload="auto" loop><source type="video/webm" src="http://web.stanford.edu/group/surf2/cgi-bin/w/wp-content/uploads/2017/05/Waves_Cut.webm"><source type="video/mp4" src="http://web.stanford.edu/group/surf2/cgi-bin/w/wp-content/uploads/2017/05/Waves_Cut.mp4"></video>
You have the webm and mp4 video which is great, and the JS looks like it is supposed to swap from image to video, but maybe it fails sometimes? I haven’t experienced it yet. Are you testing with an incognito browser?
Thanks for helping me! I do not think this is a slider plugin, but I am uncertain. If it is a slider plugin, it must have been installed before I joined. Is there an easy way to tell if it is a slider plugin or not? I just tested the website with the incognito browser, and it works—even when the normal browser does not. How can I fix this JS? Please let me know, and thanks for your help!