I'm assuming it's using the API to download captions and scanning them, which is why it'd need the Channel. It would be so hard to know where to begin without it!
Potentially future updates could search a logged in user's history?
Yep, you're exactly right. The tool works by getting the channel's videos, then fetching the voice-to-text transcripts for them, then searching within the spoken words (along with the title and description) for any keyword matches. So there isn't a feasible way to do that across all of YouTube.
I like your idea of searching the logged-in user's history! That could be handy. Another thing I've thought about is auto-importing all the channels they're subscribed to so they can search within those.
For the first version of VideoMentions Search, I kept things simple with a single "Channel URL" input field, but using their history/subscriptions is totally doable. I'll see if there's enough demand for that.
In any event, I still think that this simple first version has utility. I like being able to quickly pinpoint all the moments when a certain topic was mentioned across all of a channel's videos.
Thanks so much for taking a look, and for your feedback!
Do you keep the transcripts around on the server? It shouldn't matter much in terms of storage unless the site becomes crazy popular, so you could offer a "best effort search" or something along the lines, that just searches everything you got so far, so the site would get better and better over time.
YouTube kills your API key if you do this and make the data available (eg via API).
You're allowed to cache responses for a bit but not store them long term. "How would they know", etc of course, but if you're distributing the data they'll figure it out. Some smart cookies over there at Google.
My small website managed to get on their radar and I didn't even post it to HN!
Potentially future updates could search a logged in user's history?