How to connect video input from projector

You can go through the receiver if it has a video in along with a monitor out. If not than take the video directly to the projector from the DVD. If you have component video (red,gree,blue)on both the projector and the DVD that would be preferable over the composite video (yellow).

Take the video output directly to the projector via HDMI if you have it, otherwise component video. Take the audio directly to the receiver, HDMI, digital coax, or analog.

I use HDMI to projector for video and 7.1 analog to processor inputs set to bypass for audio. The analog audio is from an Oppo BDP-105.

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In this case, it might help if we knew what gear you are referring to.

If you have a reasonably decent 5-6 year old AV receiver, chances are you would have HDMI inputs and outputs.

If your DVD/BD player is of similar vintage, it would HDMI outputs as well. Some (like the Oppo and the flagship Sony/Panasonic etc) have dual HDMI inputs as well.

Ditto with the projector.

In this case, the solution is simple:
HDMI from DVDplayer to HDMI input of AV receiver, HDMI out from AV receiver to projector.

If you have an older DVD player that has component outputs and say coaxial/optical outputs (rather than HDMI), and your AVR supports upconversion of component to HDMI, and your projector has HDMI inputs, then:

DVD player component out to AVR component in
DVD player optical out to AVR optical in (or coax equivalents)
AVR component (or HDMI) out to projector component input (or HDMI)

There are many permutations, including using direct component connection to the projector from the DVD player (tho that limits the use of the AVR as a switch if you have multiple sources like game consoles, cable set top boxes etc).