Introduction to Video in QLab
Video in QLab is designed to be flexible and adaptable. The video workflow is intended to allow you to set up your workspace, configure your hardware, and then basically forget about it and just focus on your projection design.
Following the nomenclature of professional theater in the US, "projection" is taken to mean any form of video or film as used in a live performance. No matter whether the imagery is moving or still, digital or analogue, displayed via a projector, a TV, an LED wall, or a projection-enabled intelligent light, it's all grouped together under the name "projection design." In QLab, a Video cue is the type of cue that deals with projection. "Screen" means any physical device that displays the contents of Video cues. The words "screen" and "display" are more or less interchangeable.
QLab uses a concept called Surfaces to output video. In QLab, a surface is a sort of virtual video output which has one or more actual video screens assigned to it. By creating QLab surfaces which represent the physical surfaces on which you're displaying video (using projectors, monitors, LED walls, or anything else), QLab allows you to focus on the content of your design rather than the mechanical details of your projection system.
The idea is that each surface in a QLab workspace corresponds conceptually to a physical projection space on the stage. For example, you may be projecting onto two walls and a door, all at different angles and all covered by one projector, in which case you could create three surfaces defined in your workspace ("Stage Left Wall", "Stage Right Wall", "Door"). Or you may have four projectors edge blended on a scrim, which you wish to use as one big projection area. In that case you could create just one surface ("Scrim"). In all cases, once the surfaces are set up, you can stop thinking about projectors and simply assign your Video cues to their intended surface.
Video cues in QLab play back pre-recorded video or still image files on your computer. Camera cues play live video from webcams, Blackmagic Design video capture interfaces, and other programs on your Mac via Syphon. Text cues render styled text as still images. Once these cues are running, the imagery that they produce is all treated the same way by QLab. Each cue is assigned to a surface, and then all the cues playing simultaneously to a each surface are composited and sent to the actual physical displays.
Many media servers have ties to the cinema or broadcast worlds, in which the size and shape of a video signal conforms to an exact standard. You may be familiar with terms like "standard definition" or "1080p", and these are all terms for video standards that have specific resolutions, aspect ratios, frame rates, and other attributes. There are so many standards that it's nearly impossible to keep track.
Fortunately, QLab is completely agnostic when it comes to these matters. Video cues can play any compatible media file onto any surface, without the need to preemptively match resolution or frame rate.
When you create or edit a surface, you can set its width and height to suit your exact needs. If the surface you create is larger than the size of an image you project onto it, then the surrounding area will be filled with black pixels. If the surface is smaller than the image, the image will simply extend off the "canvas" of the surface. In either case, you can scale an individual Video cue up or down to fit on any surface.
Frame rate is another question that you pretty much don't need to worry about in QLab. Video cues can play files at any frame rate, even multiple Video cues at the same time at different frame rates, and the Mac will automatically, invisibly, seamlessly handle the necessary computation to make everything look correct.
Any device connected to your Mac which appears in the Displays section of System Preferences is available as a screen in QLab. Additionally, Blackmagic Design devices which support outputs can be used. While it's possible that USB-connected displays will also work with QLab, we do not recommend nor do we support using them. They have too many unpredictable variables to be fully reliable.
As we've said in other parts of this documentation, the secret to success with projection design is time. Give yourself time to experiment, time to troubleshoot, and time to learn the powers and limitations of your Mac.