Video Switchers: What You Need to Know

The Three Categories of Video Switchers:

To answer the question of whether switchers are necessary, we first need to break them up into a few categories: routers, seamless switchers, and broadcast switchers.

The Router

Routers are a low-cost way to clean up that mess of cables behind your video rack. They allow you to plug in all your A/V sources and destinations and route among them. The trouble with routers is that you get “glitchy” cuts only — meaning you can’t dissolve between two sources, and you’re limited to just a few resolutions. Many routers will also lose sync to the destination as it moves between sources. This causes your screen to temporarily say “No input” or flash blue for a second while it tries to re-sync to the new source. This can cause a few groans when it happens in the middle of your program.

Routers are not designed (and not recommended) for switching between video sources for “live” (IMAG) video projection. Their primary purpose is to facilitate the routing of multiple video sources and/or displays to one another off-line (i.e. not “live” or any screen viewed by an audience).

The Seamless Switcher

Most seamless switchers allow you to input all types of resolutions, and output them to a common resolution. It also synchronizes sources while you switch inputs, so you don’t have the blue screen (glitch) problem. The trouble is, except for high-end (expensive) scalers, you are limited to simply cutting, or creating simple transitions between sources such as fading in and out through black. A seamless switcher works best when you need to switch from several different graphic sources with different resolutions, all being sent to the same screen.

The Broadcast Switcher

A broadcast switcher sits at the top of the video switcher food chain. It is what you most expect to see when you step into the video room, and it is the most identifiable: it has the T-bar. A broadcast switcher allows you to send multiple inputs to multiple outputs (like a router) and allows you to create different seamless transitions between them, most importantly, cross-dissolves. It also provides more flexibility, such as the ability to key and use a DVE (Digital Video Effects).

In the professional video world you get what you pay for, and seamless switchers come in a wide range of price tags.

When Will You Need a Video Switcher?

Typically, you will need a video switcher if you have more than one source in any given program, but don’t always assume you need one. In a recent scenario, a church wanted a computer input at the booth in the back, a DVD player, and a computer input on stage. At three inputs you might jump to put in a switcher, but on a tight budget, we elected to specify a projector that could accept all three inputs because each source would be used in a different service or event.

When the youth group used the room their source was the computer at the booth, mid-week bible studies would use the DVD player, and outside groups would need the computer input on stage.

In situations like this, where only one video source is used for an entire program, a video switcher could complicate rather than simplify. It should also be noted here that switching inputs on the projector in front of an audience to access a second or even third video source is not recommended and is very distracting. Video projectors are not seamless switchers!

Cameras

Since most graphics programs now allow you to display slides, text, and videos at the same time, there isn’t as much of a need to switch between graphics sources anymore. Cameras are the big drivers of video switcher adoption now. When you have cameras — for IMAG, recording, or broadcasting/streaming — you need all the functions of the switcher such as cross-dissolves, keying, routing, and potentially DVEs.

Keying

When working with cameras, typically directors choose to insert text over the camera feeds in the form of lower thirds, which is called keying. People often only use one key at a time, but when watching news or sports on television — you will see upwards of six keys in action. A good example of a DVE is a picture-in-picture on the screen, which is helpful in scenarios where you want to split-screen two inputs or use a video switcher to create multiscreen effects.

The Difference Between Hardware and Software Switchers

The difference between hardware and software switchers used to be very clear, but many switchers are now combining the best of both worlds. Ask yourself: how do you feel about your home computer? As consumers, we have decided that we prefer the less expensive Windows or Mac operating systems, even though they have a higher failure rate than a dedicated IBM hardware server. Both can accomplish our tasks, but we accept the occasional frustration of software failure rather than using a higher-cost server like the ones built to control airplanes and other mission-critical applications.

With video switchers, you have to decide if the smaller upfront cost and increased feature sets are a good tradeoff for the occasional failure. Everyone should make a choice that is best suited to their needs.

Delay Problems

The biggest problem that a video switcher can make for a system is to add delay (aka “latency”). You’ve seen when a presenter is on stage, and all their movements are delayed a moment before showing on the screen.

Delay is measured in frames. Each video frame has two fields. Typically you have 30 frames (60 fields) per second. At about 3-4 frames of delay, the general audience will start to notice. Delay in video systems is typically caused by converting analog video signals to digital and adding un-synched devices to the signal chain.

Video Sync

Let’s talk about video sync, the heartbeat of the system by comparing your video system to a game of catch. The sync generator generates a perfect rhythm for you to catch, and then throw back at it again. Everything happens in perfect synch. The sync creates a rhythm for the whole video system so it can send and receive data at high speeds without dropping any frames.

Not all sources can accept sync, so most manufacturers have added a frame sync to their video switcher. The problem is that by syncing on the switcher you have added one frame of delay. If you can add sync directly to the device then you don’t have to add any delay.

Watch for Delay Build-Up

Converters and processors are another “primary suspect” of delay in video systems. Each time you convert the signal you are adding a half to a full frame of delay into your system. Even if the video switcher has a DVI input or something similar, you are typically adding a frame of delay by using it.

Consider this example: a church recently migrated to high definition. The church had a camera with an HDMI output. The signal was converted (1 Frame) to SDI to run the distance to the video switcher. At the video switcher, sync was applied (1 Frame) so the video switcher could accept the signal. Out of the video switcher, the signal went through a processor that converted the 16:9 camera image to 4:3 so it would look correct on the older 4:3 screens in the auditorium (2 Frames). And lastly, at the projector, the signal was converted from SDI to component (1 Frame) so the projector could accept the signal. In this scenario, you can see how quickly frames of delay add up to five. The audience notices the delay at that point. Our solution was to standardize the aspect ratio of 16:9 and SDI as the signal type to eliminate all of the conversions in the system.

Just Plan Ahead

The key is to plan without overcomplicating. A video switcher can certainly improve your workflow by keeping you from digging behind your desk for that cable you only need once a month. It can also give you a more professional look by adding in transitions and allowing you to key. Keep in mind the functionality you need as well as your long-term goals, and you will be able to determine whether a video switcher is right for you.