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DIY B4 web streaming cam research

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  • DIY B4 web streaming cam research

    Recently I've gotten interested in the B4 lens mount. It's heavily standardised, has some top quality glass available for it for sub-$100 on eBay, and supports sensor sizes between 1/1.5" and 1/2.3".

    The only people I've seen experimenting with it however have been people adapting it for micro 4/3 which is a way bigger sensor than it was designed for, resulting in vignetting. Also, there is little point in using these lenses with expensive equipment as you are better off using photographic glass for any of the old 35mm lens mounts which have huge back catalogues of second hand glass available for them.

    1/2.3" is squarely into affordable Sony IMX sensor territory though, and a lot of action cams and Aliexpress CCTV cams could be converted to the mount. However, my plan is more ambitious: I would like to build an open source camcorder with viewfinder and h.264 wifi streaming, for use at web streamed events like game speedrun marathons and hacker conventions. At least physically, it should be trivial to design a 3D printed shoulder mounted camera with a nice big battery, comfortable viewfinder and tactile buttons. Having the camera wireless allows the camera feed to be directly imported through RTSP into live streaming software like OBS without occupying USB ports or HDMI capture cards. The latency (200-400ms) can be offset by simply delaying all real-time sources by the same amount. I've done this before using a Jerry rigged camcorder-into-LKV373A setup.

    Now there are two ends which will have to meet at some point: the maker end of the spectrum, where stuff like a Raspberry Pi 3 with 7 inch touch screen would be ideally suited for the wifi streaming, viewfinder, the camera interface, and GPIO for interfacing with the B4 mount (iris/focus), and the hacker end of the spectrum, where action cams already have 75% of what we need in a single board, but are not open, so probably not suitable without skilled hacking. Somewhere in the middle of the spectrum could be MIPI-CSI2 sensor boards off Aliexpress, but those require a camera driver which is usually unavailable and covered by NDA.

    My research so far has lead to the following findings:

    The Raspberry Pi Camera 2 is an IMX219 which is 1/4" which would be too small of a sensor for B4 as the crop factor is already on the limit at 1/2.3", let alone 1/4".

    The current high-end 1/2.3" sensor by Sony is the IMX377 which is used in the Yi 4K among others, however I can't find a driver for it, and without that we are dead in the water when it comes to open source maker hardware like the Raspberry Pi. My working theory is that the sensor simply hasn't trickled down to DIY level yet, and only mass-manufacturing partners like GoPro and Xiaomi have access to the sensor so far.

    There are other possibly suitable sensors (some even 1/1.7" which is closer to the ideal 1/1.5" for B4) and it appears that there is some activity in the drone racing community, who use nvidia Tegra boards to interface with the sensors directly, so there might be open source drivers available somewhere.

    Any input is appreciated.