Most ViewSonic Projectors have a built in HDMI connector as well as A/V connectors, also known as the RCA jacks (Yellow Video input and red/white audio inputs). 

It is recommended to use an HDMI cable for better image and audio quality when possible, but RCA cables can also be used to connect a cable/satellite box, set top Box, PC, DVD, Blu-Ray or any device with a compatible source, to a projector.