I edited the config.txt file which you can find in the /boot folder, or if you put the SDCard back into your Windows PC you’ll find the file there.
The only lines I added were:
The hdmi_drive=2 forces the output to be hdmi so the Pi won’t switch to composite when the TV is still waking up.
The hdmi_mode=81 specifies the screen resolution of my TV. You need to specify this because the auto detect doesn’t seem to work when using the hdmi_drive=2 line.
To find the correct code to use for this, use the following link and look for your TV’s native resolution under the “hdmi_mode” DMT section: (You’ll need to look up in your Vizio’s specs what the native resolution is)