Video stream from usb grabber. Is it possible?

Yes, it is possible to use a USB webcam with HomeKit using a Raspberry Pi and Homebridge. Here's how:

1. Install Homebridge on your Raspberry Pi.
2. Install the homebridge-camera-ffmpeg plugin, which can convert the webcam's video stream into a format compatible with HomeKit
3. Configure the plugin with your webcam's details in the Homebridge config.json file