How to connect 4 monitors to Mac mini 2011

I want to connect 4 monitors to my Mac mini. I want to send the video output to an image wall, so the 4 monitors should show one big screen.

Which adapter(s) do I need for my plan?

An old thread, but in case anyone finds this via Google, I will be a drive-by good samaritan: I'm running 4x 1920-res monitors with a 2011 mini, as the poster wishes.

Number one is connected via HDMI; number two is connected via Thunderbolt. These two are fast enough for movies and 3D gaming. Number three and number four are connected with two USB adapters, specifically this one: HIS Multi-View II Video Adapter HMV2-MAC-PC USB to DVI Interface (link: http://www.newegg.com/Product/Product.aspx?Item=N82E16815136004 ).

Many of the other brand USB adapters won't do 1920 (check carefully) or, as someone above said, will only do a single display from OS X, but I can confirm that one (at least) works with OS X (Mountain Lion, though I also used this setup with Lion).

This device:

http://www.atlona.com/ATLONA-2ND-GENERATION-USB-TO-HDMI-CONVERTER.html

Allows up to four additional displays on a mac. It won't run 1080p30 due to USB limitations, so you need to choose a lower resolution if you need high framerates, however it does get 10-15 frames per second at 1080p resolution, so for many applications it's suitable. It will run 720p resolution at close to 30 frames per second. There are other similar adaptors, but you'll have to look carefully for one that supports more than one device on the Mac. I've run into some that support multiple displays on windows, but only one on OS X.

It puts a heavy load on the computer though, so you'll need a new mac mini, the older ones will have trouble running more than one at a reasonable video framerate.

Also, no USB video adaptors that I've tested for the mac allow OpenGL or 2D acceleration. This is likely due to Apple's restrictions on their video acceleration API - most only run in the rather limited framebuffer mode. You can get Quicktime to display video, but you won't be able to run keynote presentations or iPhoto on the USB video adaptors.

If you need full video, or the software you're running requires 2D acceleration or OpeGL, you might be better of with a video splitter that takes the onboard video and splits it into several monitors. There are many devices that do that, search google for "video wall." You'll have to settle for lower resolution, but if you're running video you probably need the framerate more than the resolution anyway.