Using the Sony a6600 as a Webcam on Linux
For decent instructions, visit this page. Recording what I care about here: Sony alpha cameras allow you to output a compressed image stream over USB. Basically it sends JPG images (1024x680) continuously. My understanding is that whatever path generates these images is repurposed from the path that outputs viewfinder images.
This has obvious limitations, like you won’t be able to record 4k video from your camera directly to your PC. You also won’t be able to get the audio stream.
My experience with this also introduced some video lag. While I haven’t tested it, I suspect it’s possible there will be lag between the video (from camera) and audio (from my actual webcam mic).
If you want to really capture 1080p @ 60 or 4k video, you need to buy an HDMI capture card which gets the raw video stream from HDMI and encodes it back into a video file. Capture cards also let you get audio. OBS Studio lets you add both a V4L2 capture device for the video and a PulseAudio audio capture device that uses the same capture card.
The most popular HDMI capture cards are made by a company called Elgato, but they are like $100. You can get one that does 1080p @ 30hz for extremely cheap (under $20). Here’s one I got.