The official download option offered by TED Talks website only gets you a 480p download maximally, and if you want to download the video as an MP3 file, it is only in 80 kbps. If you want better than that, you need a 3rd-party TED video downloader like DVDFab Video Downloader which can get you the TED talks videos at their original quality, most of which are 720p. And with an AI upscaling software, you can easily upscale 720p videos to 1080p or even 4K quality.