I'm building a thing that tells people when a YouTube stream goes live. In order to build this, I need to know when a stream goes live, be it via push notification, polling, or some other method.
With Twitch, it's dead easy. All you have to do is send a GET to https://api.twitch.tv/kraken/streams/[STREAMER_USERNAME_HERE] and you get a JSON object with everything you'd ever hope to know (try it in your browser, it's great). I have combed through the YouTube Streaming and Data API's and nothing even close to this feature seems to exist.
I know that something, somewhere is alerting something when a stream goes live, because my phone gets a notification when the people I am subscribed to start streaming. But if there are no public calls in the API, I'm left with no other option than scraping the HTML off a page every couple seconds, which is bad for both me and YouTube.
Further on this, YouTube's push notification API for regular videos famously doesn't work [1] [2] [3] [4], and every dev is left to either use the deprecated XML feeds (which update sometimes up to an hour slow) or scrape HTML off youtube.com pages (the only current solution for instant updates). So, even if there's something off the API that I missed, it's moot if it doesn't actually work.
That said, am I missing something? Is it possible to get a notification if a stream goes live? It's kind of a deal-breaker for YouTube vs Twitch if there isn't.
It is currently not possible to do what you are asking with the public YouTube API.
You can only retrieve information about your own liveStream or liveBroadcast objects, not anyone else's. Additionally, there is no public API to get a notification when another user goes live.