I'm not aware of any way to do so directly. There isn't any RTSP support. Some of the home automation hubs (like Home Assistant or HomeKit) might be able to do so. One thing to keep in mind, though - this is a Battery Doorbell. Even while wired, it runs off of the battery and only trickle charges (at a fairly low rate) from the doorbell A/C wiring. See the linked support article below. That article is mostly about cold weather performance, but it also mentions the trickle charging only design. As such, if you pull video all the time from this doorbell to a NAS, it will deplete to zero pretty quickly. A day or less, I would imagine...maybe just hours. You can't use this model as a 24x7 device, like you could with the Nest Hello. It designed to be an "event capture" type device.
https://support.google.com/googlenest/answer/11830989
The specific reference from that article:
Nest Doorbell (battery)
If you’ve connected your Nest Doorbell (battery) to your existing doorbell wiring, the wires don’t directly power the doorbell. Instead, the battery is trickle charged by the power that comes through the wires, and the doorbell runs off the battery charge. At temperatures between -4°F (-20°C) and 32°F (0°C), the doorbell can continue to work, but the battery will drain because it can’t be charged. If the battery drains completely, the doorbell will shut down, and you’ll need to bring it inside to be charged.
