2021 update: On YouTube, click the three dots “…” to the right of the Share, Save items, and click ‘Open Transcript’. ✨
2020 update: this method no longer works. Services like downsub.com may work instead.
The automatic transcription of YouTube vidoes is pretty amazing, and sometimes histerical at times.
However, if for some reason you want to get a raw copy of the automatic (and possibly manual) youtube captions, you simply use the TTS_URL key of the yt and append some magic URL parameters: &kind=asr&fmt=srv1&lang=en.
The following JavaScript will automatically redirect you to the xml file of the transcription:
if(yt.config_.TTS_URL.length) window.location.href=yt.config_.TTS_URL+"&kind=asr&fmt=srv1&lang=en"