This is a comparison of all currently (October 2019) available Nano sized video transmitters. To qualify for this list the vide transmitter has to weigh less than 5g. Further it must be possible to adjust the video transmitters settings either via Smart Audio or IRC Tramp protocol.

* The weight is without the case, it can be removed easily. With the white case it weighs in at 4.2g. You can choose on the cam itself if you want to use it in NTSC or PAL mode by making a solder bridge.