As far as I can tell, Google (but not YouTube?) does search YouTube transcripts. I have successfully Googled text in a video's transcript and found that video.

As far as I can tell, Google (but not YouTube?) does search YouTube transcripts. I have successfully Googled text in a video's transcript and found that video. The transcripts themselves are pretty bad though (Google's using old tech). They're usually good enough for auto-summarization though.