I'm assuming they are using the YouTube API to access the captions, but what special sauce are they using? Some special partner key? An different API version? Are they just scraping from the videos themselves or something? The request might not be properly authorized, or the video order might not have enabled third-party contributions for this caption. In other words, when I access the YouTube API myself (even with youtubepartner and youtube.force-ssl scopes), I can only download the captions of some videos, but when I try the same videos that failed for me with 403: The permissions associated with the request are not sufficient to download the caption track.

This is somewhat of a duplicate question of Does YouTube API forbid to download video captions if you are not it's owner?, Get YouTube captions and Does YouTube API forbid to download video captions if you are not it's owner?, which all basically say it's not possible unless to download captions via the YouTube API unless you are the owner or third-party contributions are not enabled however, my question is how to sites like or have access to all captions?

Downsubs youtube