Some of the ted videos or accounts are private and some videos are geographically restricted by the owner. We cannot access these ted videos, thus they cannot be downloaded.
When you left click on the download link it is normal the browser starts to play ted video. You need to right click on download link and choose "save as" to save the ted video.
On a PC, they are usually saved under "Downloads" folder. On IOS and android devices you can save ted videos to browser download folder or directly to Photos app.
Most of the ted videos we serve are in HD or Full HD format. This means that you can download highest quality ted videos including 1080p ted videos and 720p ted videos.
Most of the ted videos are already in mp4 format, we automatically convert and serve ted to mp4 instantly if they are in different formats. You don't have to manually convert ted videos to download in mp4