Module 60


Updated: 01/14/2017

Module 60








Video Switchers

and Visual Effects

In this module we will cover:

  • Hardware and software based video switchers

  • Video switcher functions and controls

  • Some basic ▲ visual effects (VFX)

  • Supers (superimpositions)

  • Luminance and chroma keying 

  • Multi-view monitors

We'll start with a very basic switcher configuration.

 Fader bars

Each button represents a video source—even "black," which includes the technical parts of the video signal necessary to produce stable black.

The bottom row of buttons (outlined in blue) represents the program bus or direct-take bus.

Any button pressed on this row sends that video source directly to line out, the final feed being broadcast or recorded.

The easiest way to instantly cut from one video source to another is simply to select it ("punch it up") on the program bus. The program bus generally handles more than 90% of video switching.

But, what if you want to dissolve (fade) from one camera to another, or fade to black?

For this you need to move to the top two rows of buttons referred to as effects, or the mix/effect bus. From here, with the help of the fader bars, you can create rudimentary visual effects.

fader bars 2 When the fader bars are in the top position as shown here, any video source punched up on the top row of buttons is sent to the effects button on the program bus. (To see this clearly, you may want to refer back to the larger illustration above.) The buttons that have been selected are shown in red.

In this case, camera 3 was selected on the effects bus, so that's the camera that will be sent down to the program bus. Since the effects bus has been selected on the program bus, its signal will then be sent out and be displayed on to the line out video monitor.

Put another way, if the fader bars point toward the top row of buttons on the effects bus, and camera 3 has been selected on that bus, we will see camera 3 when the effects bus is selected on the program bus.

If we were to move the fader bars down to the lower position, the video source selected on the lower row of buttons (in this case camera #2) would be sent to the program bus.

During the process of moving the fader bars from the fader bars 3 top to the bottom, we see a dissolve (and overlapping transition) from camera #3 to camera #2.

If we stop the fader bars midway between the move from top to bottom, we would see both sources of video at the same time — we would be superimposing one camera over the other.

Although this used to be the way we displayed titles, credits, etc., on the screen, today we use an electronic keying process.

As illustrated below, a key represents a much cleaner and sharper effect.

key and super  

effects bus  

First, note in the drawing above that the fader bars have been split—each one being at the "0" (no video, or black) position. If we were to move fader bar "A" to the top position we would put camera 3 on the air; if we were move fader bar "B" to the bottom position we would put camera 2 on the air. But, of course, you already knew that.

What you don't want to do is split the bars so that they each sends out maximum video from its source. (With 200% video being sent out video engineers may get upset with you!)

Next, note the extra row of buttons (outlined in green) marked "preview," just below the program bus.

With the preview bus we can set up and check an effect on a special preview monitor prior to switching it up on the program bus. Without being able to preview and adjust video sources before putting them on the air, we might end up with some unpleasant surprises.

To see (preview) an effect, we first punch up effects on the preview bus. When we get the effect we want on the effects bus, we can cut directly to it by punching up effects on the program bus.

Some switchers, like the one shown in the photo at the beginning of this module, have multiple effects banks. A simple version is shown below.

effects bus

Using what you know about switchers at this point can you figure out how black arrived on the screen in the drawing above?

If you moved the fader bars on Effects #2 to the up position, you would make a transition from black to whatever was on Effects #1. In this case it would be Camera 2 superimposed over Camera 3.

Finally, let's add a few bells and whistles. wipes

The top row of buttons  in this drawing represents various types of wipes.

Yellow on the buttons represents one video source, black another.

Additional patterns—some switchers have dozens—can be selected by entering numbers on the keypad.

If wipe is selected on the switcher, the button pushed (indicated in red in this drawing) shows the moving pattern (controlled by the fader bars) that would be involved in the transition from one video source to the other.

A border along the edges of the wipe pattern — a transition border — can be used and its hue, brightness, sharpness, width, and color saturation selected.

The key clip knob controls the video level of the source you are going to key into background video. This is adjusted visually on the preview monitor.

Downstream keyers, which are often used to key in such things as opening titles and closing credits, are external (downstream from) the basic switcher.

The advantage of a downstream keyer is that it doesn't require the use a switcher's effects bank for switcher

This means that the bank stays free to be used for other things.

The switcher shown at the left incorporates versions of all of the features we've discussed, plus a computer display that adds even more options.

Although switcher configurations differ, they all center around the same basic concepts.

In recent years switchers have been getting more compact, bringing many video control functions into a "small footprint."Simple Switcher

The switcher on the right has many of the features of the larger switchers, including limited visual effects.

Although it may not be as impressive looking as some of the larger switchers, it can adequately handle the needs of many small studios and production facilities.

Multiview Screens

Until recently, each video source in a TV control room was displayed on a separate monitor. This meant that control rooms typically had dozens of TV monitors, taking up considerable space. In the case of tube-based monitors they also consumed a lot of power, generated heat, and taxed air conditioning.

Multiview Monitor.

With the introduction of large, flatscreen monitors in the 1990s, this started to change. As shown on the left, today's video switchers can output multiple video sources for a single display.

A typical multiview display suitable for the technical director or director is ▲ shown in this pop-up photo.

Although there may be a large flatscreen display at the front of the control room, crew members, such as the TD and audio person, may have smaller displays directly in front of them.

Depending on the needs of specific productions, template configurations (display arrangements) can be programmed into the multiview display or switcher with macros (generated computer code) and called up as necessary. Video source boxes can also be rearranged on the display by dragging them into different positions with a mouse.

The corresponding video sources can be selected by using a standard switcher, with a mouse, or in the case of touch-screen displays simply by touching the desired source.

Many of today's switchers use macros to program complex special effect sequences and even CG information.

Some switchers allow for the storage of clips (audio and video segments) that can be inserted into programming as needed.


Chroma Key

Earlier, we mentioned luminance keys, where the keying effect is activated by the brightness or luminance of the video that you are keying in. But, as we saw when we discussed virtual reality sets, it's also possible to base keying on color (chroma).

In chromakey a particular color is selected for removal and another video source is substituted in its place.

weathercaster using chroma keyThis type of keying is commonly done during weathercasts where a graphic is inserted behind weather person. (Note photo above.)

In this picture the man on camera is looking at a monitor off-camera on our left, using it as a guide to know where to point on the green chromakey background. The result is shown on the HDTV monitor at the right of the photo.

Although any color can theoretically be used in chromakey, royal blue and a saturated green are the most commonly used. Most of the visual effects we seen video production are done with chromakey.


Software-Based Switchers and Effects

Most software-based switchers use the hardware-based switcher that we've discussed as a graphical model.

 Tri caster Switcher

The NewTec TriCaster Studio™ above is a long way from ▲ the first-generation software based systems of 20 years ago. The system illustrated above requires a shoe box-sized interface and the output and can be displayed on a laptop or desktop computer and controlled by a keyboard and mouse.

Software based systems can be easily and regularly upgraded when new software is written — an advantage you don't have to the same degree with hardware-based equipment.

With most software-based systems it's also possible to go far beyond basic switching and create a wide variety of visual effects.

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