I have a YouTube video which still loads and plays because I opened it before removing by the user.
It is still on googlevideo.com and I can see links in the "stats for nerds" and umatrix.
How can I download it?
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Sign up to join this communityBest way to achieve this, in my humble opinion, is via screen capture.
As above, Google stores videos in such a way that it's not straightforward or easy to extract from session level/cache data
If you still have it cached, you may be able to retrieve it by digging around in wherever your browser stores cached content. However, since YouTube doesn't store videos as one big file but rather in a couple second long chunks that then get stitched together (-> Dynamic Adaptive Streaming over HTTP), you probably won't find any convenient way to get them into a usable state (especially if your browser includes the HTTP headers in the cache).
As for "stats for nerds" and umatrix: What you're seeing there probably also is cached.