YouTube Captions help ranking

I just found something cool that's been talked about before on the forum but never really "confirmed".

i45.tinypic(.)co|m/a4suu8.png

This is YouTube using captions in their SERP algorithm. Can't post images yet.

Time to start stuffing captions with keywords?

what is SERP algorithm and I'm confused on how you confirmed it?
Might be a noob for asking these questions but this interests me a lot.
i have almost 15,000 subscribers and lots of videos. adding captions to each video will take forever if its not going to help really.
So how exactly will this help the video?
thanks

Highly doubt it helps, the video has 400k views so chances are that video was posted in a community where people like that shit and then grew views and thus grew in rank. I have captioned videos that have the same SERP rank as my othe videos with no captions.