I have a Nexus 5 that I'd like to use for some video recording. The meetings I'd like to record are likely to run long enough that they might cause my phone to run out of space mid-recording. I am wondering whether it is possible to connect my phone to my Macbook (or some other device) such that the file is written directly to my Macbook SSD while recording; in other words, to use the phone as a peripheral. Is this possible?
As I mentioned in the comments, you can use IP webcam apps on Play Store and then turn your mobile easily into a webcam and record your computer's screen using a video recording software. This way you can rely on your computer's memory instead of your mobile's storage(which is limited in most cases). Now you can use your phone as a webcam peripheral device and recording videos directly in your Macbook's SSD storage. Some apps provide functions to add a server and upload the videos to cloud.
Note: Most app requires an USB cable connection or that you have your mobile and computer connected to the same network which is why it named IP webcam since it is accessed using the IP address generated from the connected network.