Convert youtube video to MPEG-4

Hi. I dont have the time to maintain an aquarium. I find the gentle movement relaxing like white noise. I thought it would be nice to have a video of moon jelly fish loop on a digital photo frame. I bought one that supports video. Most I have found online play MPEG-4. I plan to take videos off of youtube. I want to know how to download and convert the video this way I can change my picture frame as I like. Ive tried googling and downloading things off Cnet. I would rather pay for the answer then to keep downloading things that dont work. Its confusing because there is MP4 and MPEG4 and alot of the conversion programs seems specific for certain devices of apple vs android etc. This is the frame i ordered. [login to view URL] The video Im trying [login to view URL] I already deleted the websites and conversion programs I tried without success so I unfortunately cant provide those as reference. I know some programs on Cnet require a small fee for full version. I wouldnt mind paying. Im just cautious getting full before knowing it works and havent figured out the using the trial versions. I want to upload one of the files I made with the program that doesnt work but it says its too big. I assume this is a very easy job for someone that knows what to recommend. I just dont have much time at the moment to search and my computer knowledge is very basic. I put it as Micro job for this reason. If its not fair let me know