Whoops! steganography -> stenography
I think we can all relax about the throwaway example he tossed out there about coding with steganography. We can all see how it's a bad idea, so the 20 people who've made that same point now can rest assured that their unique insight is appreciated.
I would've loved to be able to do ~180 wpm when taking notes in university. For me, notes will always be far better than a recording because they're much easier to skim than video. Also the act of noting increases retention, and you can choose what is worth writing down and insert add your own thoughts or questions live, rather than by reviewing the video later (which, given the time crunch of university, usually doesn't/can't happen). This is why I still take notes, even while also recording audio to catch the sentences that I inevitably can't transcribe in time.
If there was some note-taking app that let you type steganographically, draw on the notes, and insert photos (e.g. of the whiteboard) in-line as you take them, that honestly would be a killer app that I'd invest time learning steganography for. (The time would come out of my Duolinguo budget; sorry France!