videos turned into jpegs when copied from Photos to dropbox

I created a 'favorites' folder in Photos of 1000 images and videos from many years of images - then attempted to select all and copy (using dropdown menu in photos) these files to my dropbox account. All of the jpegs were sized down and all of the videos were turned into jpegs - any idea why this would be happening and a way to fix it? below is my post to the dropbox forum, they are saying that it couldn't be dropbox doing this? I first had tried to just make this favorites folder a shared folder, however i can't download the videos to my phone for use on instagram, etc that way... only images. which is really annoying, btw! 🙂 i was trying to save room on my phone by doing all this but i keep running up against roadblocks! help!