Here's my attempt at creating a grainy video effect in the browser using a media stream (from the device's camera - the page should ask for permission first). Very much an MVP; I'm already working on making the dithering algorithm more efficient. https://codepen.io/kaliedarik/pen/OJOaOZz
> YouTube's already got some limited interactivity features, DVDs had them, why not all videos?
I don't know about videos, but again this is doable in the browser using the canvas. For instance, this example: https://scrawl-v8.rikweb.org.uk/demo/canvas-027.html - the swans, and both geese, are clickable (to their respective Wikipedia pages). The navigation around each goose is a clickable box, while the navigation on the swans uses a chroma-key effect to limit the clickable area.
But there is definitely a trend towards more customizable decoders, with a larger set of primitive operations (DCT, motion estimation/compensation, convolution filters) and parameters. The codec space is slowly moving towards a model where the decoders are VM highly optimized for specific tasks.
You could do things like 480p training videos with ultra-crisp text, and snow/fire/etc effects.
You'd probably have to prevent it from having network access or else you'd just be asking for the videos to rot over time, but you could give them an embedding API or even access to a few small bits of data, so you could have a YouTube video that changes with seasons and location.
If you were strict about the no network access thing you could give access to all sensors, since the data would never leave the device.
YouTube's already got some limited interactivity features, DVDs had them, why not all videos? It would mostly be a novelty, but you could also do really cool stuff like use Bluetooth beacons to skip around to certain parts for an interactive tour, although you might have to enforce downloading the whole thing before playing if you wanted 100% no privacy leaks.