Zipped SD Card image for the BATC Video Source for the Raspberry Pi Zero. Simply download and unzip vidsource.zip, write the image to the card using Win32DiskImager, and then put the card in a Raspberry Pi Zero, 1 to or 3 (not 4). Note that the download is 1 GB and the image is 3 GB so you will need just over 4 GB of disk space (which can be cleared after you have written the SD Card).
System will boot and output a Test Card on the composite video output. Connect a push button between GPIOs 18 and 20 (=ground) to cycle between the available cards, and connect pin 16 to pin 14 (=ground) to select the Pi Camera. Edit text files in /boot/testcard/ (use sudo nano) to change the captions.