Captionfy.io

Captionfy is a free Youtube community captions platform with a subtitles/captions editor that you can use to create captions for any public Youtube video. You can then download the subtitles file, share the Captionfy video page with the captions (using the original Youtube video embed), and provide the Youtuber with a link to the video to download the captions and publish them on Youtube.

Captionfy doesn't have a direct sync with the Youtube video once captions for it are made. The captions will only be available on Youtube once the Youtuber downloads them from Captionfy and puts them on Youtube. However, anyone can watch the captioned video via Captionfy and share that page to anyone who needs the captions. Every Youtube video on Captionfy is embedded from Youtube, so the views are correctly made for that video on Youtube.