Amara is the same service referenced in our lesson about creating captions using the subtitle creation tool. The difference is that with YouTube and other third-party sites, your video is already uploaded to the Internet, so to create captions, all you need is the URL to the video.
Amara subtitles videos created with supported video types. Additionally, the video must be publicly accessible and hosted on supported third-party sites. Amara exports to a variety of file types, including WebVTT and SRT.