I've seen in /boot/boot.cmd how it should be changed but the video output is a work in progress:
https://linux-sunxi.org/Mainline_U-boot#FB_console

Hello, How can I get video output from the CVB pin? I tried to connect a TV set with composite video input but i get "No signal" on the screen. I can access the nanopi through the serial console. I have searched info on activating the video output with no success. Also I've seen in the npi...