Every time you upload a video, YouTube tries to generate a caption file. If there's audible text, you can grab a subtitle file within a few minutes of uploading the video.
But how's the quality? Pretty mediocre! It's about as good as you'd expect from a free machine-generated transcript. The caption files have no punctuation between sentences, speakers aren't broken out separately, and errors are very common.
But if you're transcribing interviews, it's often easier to edit a flawed transcript than starting from scratch. And YouTube provides a solid interface for editing your transcript audio and getting the results in plaintext.