This happened to my heater this year. We paid somebody $150 to fix it. Do not run your heater, until it is fixed. What's happened is you most likely have a clog in either your burners, or your heat exchanger. They need to be cleaned, in order to get that flame back inside where needs to go. The little white and red fuse looking device at the top left of your video is a fusible link. When the flames touch that it will shut your heater down, and will not work without replacing that piece. Best thing to do is run a coat hanger or heavy wire through all the burners to remove any cobwebs. Then if you were able to pull apart to look at the heat exchanger it either needs be cleaned on top of which can be done with just a brush and some water. If that doesn't fix it, the heat exchange will need to be pulled out, which is doable but it's a big job. Pulling the exchanger out is the only way you can clean the bottom of the heat exchanger. There are a lot of things you can break while doing this job, so if you're not comfortable or experienced I suggest you hire professional to fix this. It was the first time I had taken apart, so I had a professional to help me. Next time I will do it myself. it is mostly just screws, but you have to be very careful how you raise the heat exchanger so you do not damage the fireproof coating inside. The pool guy told me that the heat exchanger was blocked not allowing the hot gases to escape, so the gasses pushed the flames out under the front panel. Fusible link is there because this is quite common, and it is to prevent heater from catching fire.