An intriguing feature introduced in version 2 of Apple's Motion Apple's Motion is the ability to control it via MIDI: the Musical Instrument Digital Interface. This allows users to choose among a wide variety of third-party input devices to edit parameters in Motion - such as scale, opacity, rotation, or most effect parameters - either while parked on a still frame, or while previewing in real time. The user's gestures can also be recorded in real time, allowing you to "perform" parameter edits, reacting to the video or soundtrack. This capability has also caught the attention of the VJ (video jockey) market, giving them another tool to perform video transformations in real time.
As MIDI is a specification that grew out of the music rather than video industry, the idea of controlling Motion with MIDI may not be entirely intuitive. We'll demystify the subject here, giving specific steps and advice on how to get the most out of the marriage between the two. We'll also review a variety of MIDI control surfaces which are well-suited to this task. Although the most common image of a MIDI controller is that of a small piano-style keyboard, there is quite a variety of control surfaces consisting of knobs or sliders, which make them ideal controls surfaces to interactively enter parameters for a software program.
(If you are new to the subjects of either MIDI or Motion, go to the last page of this article, which contains companion sidebars on these subjects.)
Speaking MIDI to a Mac
To control Motion via MIDI, first you have to figure out how to get MIDI messages into your Mac. Some MIDI control surfaces now have USB interfaces, which make the task easy: Merely connect the MIDI controller to a USB port, and install any drivers that may be required. If your controller only has MIDI physical connections, you will need to connect some device that includes a MIDI interface to your computer, install its drivers, and connect everyone together. Although the Mac has an Audio MIDI Setup utility, you do not need to use this; Motion will automatically detect incoming MIDI messages.
MIDI control surfaces (reviewed on page 4) often have a variety of ways they can be configured, which determines precisely which MIDI messages are sent when you move a slider, knob, switch, or key. The best option is to send MIDI Continuous Controllers (although Motion will also respond to Note On/Off messages - see the section at the bottom of page 4 titled Trigger Finger). These controllers also offer the option of what MIDI Channel to send messages over; this is akin to a device ID. Motion 2 ignores the MIDI Channel, treating all equally. Therefore, don't rely on MIDI Channels to differentiate one knob from another - instead, choose or program a configuration where different controller numbers are sent for each knob or slider.
Getting Motion to hear MIDI
MIDI control is consider a behavior that you add to a parameter inside Motion. However, MIDI does not appear under the Behaviors icon above Motion's canvas - this is because it must be applied to a specific parameter of an object, Filter, Emitter, or Replicator rather than to an entire object.
Once you have your MIDI control surface hooked up, select an object in Motion, click on the Inspector tab, and then click on the Properties tab (the shortcut is F1). If you want to control a Filter or other modifier, open its respective Inspector. Then either Control+click or right-click on the name for a parameter -say, Shear. In the popup menu which appears, select the second item: MIDI (see the figure at right) The Behaviors pane will open with a behavior named MIDI selected; if you have Dashboards enabled (F7), it will switch to MIDI as well.
Make sure the Control Type in either the Behaviors panel or Dashboard is set to Learning, and then move the knob or slider on your control surface that you wish to use to edit this parameter. If your controller is properly connected, the Control Type popup will change to Controller (or Note, if you hit a key or strike pad on your device), ID will change to match the number of the controller you are moving, and Value will update as you move the control. You should also see the selected object change in your work area. You can set these values manually - as well as the Apply To target for the control - but it is far easier to use Motion's automatic Learning mode.
You can assign additional MIDI controllers to additional parameters. All will be named MIDI with a number appended to their end; to reduce confusion, double-click on the name MIDI in the Layers panel (opened using F5 or Command+4), and rename each control behavior to something more descriptive such as the name of the parameter being controlled.