Analog Video Output
Software update 201707120 introduces an Analog PAL Video Output mode. In update 201707311 audio routing from the USB microphone to the RPi audio output was added. This mode is particularly useful for driving analog video transmitters when operating portable without the need for an additional camera, test card generator or microphone. This is especially true for the 5.6GHz FPV transmitter shown elsewhere on the Wiki.
The Composite video output mode can be selected from the "Output" menu on the console, or from Menu 2 on the touchscreen.
Note that the video on the analog output is smooth, not jerky like the viewfinder which is limited to a slow refresh rate.
Rather than reproduce the connection details, here is a link to a good website describing the pin connections on the 4-terminal 3.5mm jack. http://www.instructables.com/id/Raspberry-Pi-2-Quick-n-Easy-RCA/ It should be noted that there is no standard connection for this jack - do not assume that the lead you have in the junk box will be correct! The G8GKQ Portsdown transmitter seen at CAT17 had back panel BNC connector for video and 2 RCA sockets for audio connected to the Pi via a TRRS jack in this way.