Recently I had two matched projectors for a couple of hours, so I decided to try and achieve a seamless scrolling effect with live camera sources.

Through luck rather than planning, all of my video cameras are from Sony, and they all have the same type of cable for composite analog-out. Looking for better quality, I picked up half a dozen of these replacement cables, which have both S-Video and Composite jacks. This allows me to send a single camera output to 2 separate layers, setting the stage for some multi-screen spanning.

The Setup

Put the VJX into Battle Mode (Menu > Video > Mixmode > Battle 2*2)
Set Outputs for separate projectors (Menu > Video > Outputs > Choose “Master 1″ for first projector, “Master 2″ for second)

Plug one output from each camera into each side of the mixer:
Camera 1:
Composite Output - Track 1, Input 1
S-Video Output - Track 3, Input 3
Camera 2:
Composite Output - Track 2, Input 1
S-Video Output - Track 4, Input 3
… and then hold down the “Input” button and select these inputs.
For each track in turn:
Enable Background Alpha
Enable Scroll FX

Midi Control

The VJX has a complete midi map, covering almost every function available (apart from saving and loading of presets). The VJX has a pretty intuitive control setup for the huge amount of options available, but it would be physically impossible to control independent parameters for 4 tracks concurrently, which is where external midi enters the picture.

This particular setup used Ableton Live to take care of the midi messages, but you could use anything which is capable of sending midi CCs on specific channels.

(Download the Live project here -  Vixid Projector Spanning.zip - very simple, but it does the job)

This is setup for vertical scrolling, so each channel is sending CC5, which controls the “Scroll Y” parameter on the VJX. When “Scroll Y” is at 0, the layer is scrolled off the top of the canvas and not visible, when it’s at 63 it’s centered, and 127 is scrolled off the bottom of the canvas. To create the seamless scrolling effect we simply offset the inputs for each camera, so Camera 1’s Composite output scrolls down across Projector 1, then as it disappears off Projector 1, the S-Video output starts to appear on Projector 2, giving the appearance of a single, smoothly-scrolling image.

Bugs and Limitations

You’ll notice that slow scrolling in the video is a little jerky. This is because I was only using course midi control - cutting the scroll range (around 1152 pixels) into 128 chunks gives us 9 pixels per single CC value. The VJX understands 14-bit, high resolution midi, and so is capable of perfectly smooth scrolling if you send it high resolution messages.

Also, because of the “Battle Mode” setup, this technique is also limited to “just” 2 projectors. The VJX does have 3 separate outputs, but this technique requires all 3 outputs to have 2 layers active at once. However, there’s nothing stopping you from adding extra cameras or video sources to the mix, as long as it can output S-Video and Composite concurrently, it will work.

You’re looking at that Macbook video adapter a little differently now, aren’t you?