Video wall processors tend to be rather expensive as they each need scalers in them and are purpose built to do what you are talking about.
If you don't have the TVs already, it's actually far more price effective to purchase televisions which already have this capability built in. Since all TVs these days have built in scalers, it is a minor cost increase to add the scaling necessary for them to act as part of a video wall.
You would then use a standard 1x4 splitter, and feed the same signal to all four displays, and each display will cut out the portion it needs to display. Many of these displays allow for setups from 2x2 up to 4x4 or 5x5 video walls.
You would need to dig through the displays which are out there to achieve this, but something like this can do up to a 10x10 video wall (100 displays).http://www.samsung.com/us/business/displays/digital-signage/LH46UECPLGC/ZA
They also have ultra narrow bezel displays which work better in this type of setup.
Overall on cost, if you already have the displays and just want to feed it a video from a USB drive source, it is far less money to actually get a small PC with video cards which can support up to four displays. This way you allow the video cards in the PC (inexpensive) to handle all the scaling and processing.
Understand, that there are products like this:http://www.gefen.com/kvm/ext-hd-vwc-144.jsp?prod_id=14708
It's about $1,700 on their website, and Gefen is a fairly solid and middle-of-the-road priced company on their products. You may find it for about $1,100 or so online.https://www.google.com/shopping/product/17112820128743495277?q=EXT-HD-VWC-144
If you want to Google it, you are looking to setup (I assume) a 2x2 video wall. So search '2x2 video wall processor'.
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