If you use the "Picture URL" box to include a link, the URL must end with .jpg, .jpeg, .png, .gif and maybe a few others.  Any modifiers after .jpg must be deleted.  
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E.g., If you cut and paste this URL https://static-b.imgix.net/starfish.png?w=150&h=150 into a browser, you get a perfectly good picture. However, it will produce an error message if pasted into the TER Picture URL box.  Delete the "?w=150&h=150" to get this URL ending in .png https://static-b.imgix.net/starfish.png and it will post OK on TER.  
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Video files have non-allowed file extensions (.mp4, .mov, etc.) and should NOT work in the Picture URL box. (But I haven't tested it.)
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As mrfisher suggested, upload your video file to a hosting website (youtube, etc.) and post the link as a "regular" link in the "Link URL" box. Put a title in the "Link Title" box ("My hot video") and I think that should work.  
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You can actually post a video URL in the "Link URL" box and a static image (.png, .jpg, ...) in the "Picture URL"box as sort of a Preview of the Link (or a diversion). I am posting a static image of a fish (no relation to mrfisher) which may or may not be related to the Video link also provided. The way TER has it set up, the image itself becomes a Hot Link to the URL provided.  
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After you submit your post, go "Back to thread" and give it a test. If it's not the effect you were expecting (the video itself or the page with the video), Edit your post and the URL and try some variations.  
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I suggest posting the link to the PAGE with the video and not the video itself which might start playing by itself (autoplay).  "NSFW" is a warning that the link or content is "Not Safe For Work" which always means "Not Safe For Working At Home with lots of other people, such as family, kids, neighbors around."