Vudu might not be the most popular video streaming service, but it's more useful on the SHIELD starting today. The app now has support for Google Assistant commands, and the SHIELD can output HDR video from Vudu. Of course, you'll need to own some HDR content on Vudu first.
You can start a Vudu voice command by pressing the button on your remote or by speaking the hot word, assuming you've set that up. Vudu can understand basic playback controls like pause, rewind 5 minutes, and so on. If you don't have the app open, you can also ask Assistant to play content in Vudu ("Play [a thing] in Vudu").
4K content has been available on the SHIELD via Vudu previously. The new wrinkle in this update is support for HDR 4K video. The SHIELD is one of the few boxes that can output HDR, but you will also need an HDR-capable TV. If you're all set on that front, update the Vudu app and you're good to go.