What does the weather forecast on your local TV station have in common with a $300 million blockbuster? Believe it or not, they both use the same visual effect. It’s what you know as a green screen, although it doesn’t have to be green at all. The technical term for it is “chroma keying.”
You probably already have an idea how to use a green screen, at least in principle. You film something or someone in front of a colored background — the green screen. Later, you replace everything that’s in the color of the screen with other footage, images, charts, presentations — whatever visuals you want.
Chroma keying a live stream works almost the same. The main difference is that you have to replace the green screen as you’re filming. It’s really easy to do — we’ll guide you through it and help you grasp chroma keying in OBS.
Why is chroma keying so popular?
Green screening is an extremely popular technique that originated in movie making. The big Hollywood movie productions use it, as do small independent movies. Chroma keying is what really helps directors and creative teams achieve their vision, and it’s responsible for some of the most memorable moments in cinema.
It’s also about saving money, though. Using a green screen can be cheaper than building real movie sets. It’s sometimes less expensive than organizing production in real places — traveling, insurance, and filming licenses cost money.
Plus, it’s often much safer for actors to do seemingly dangerous stunts in front of a green screen than in genuinely dangerous locations. Sometimes, though, even mundane things like driving a car are filmed in front of a green screen to make them safer and less demanding.
The use of a green screen in live streaming
But you’re not making movies, right? It’s not that likely that the use of chroma keying can save you a ton of production money. You’re probably sensible enough to avoid doing dangerous things in your streams, too. So why would you need a green screen for a live stream?
Chroma keying has many great applications in live streaming, such as:
- It makes you independent of your location. You can stream from any location where you can set up a green screen and have the same visuals in the background. The background visuals are added independently.
- The background can change during the stream. You don’t have to stick to one background. You can change it according to the topic, your script, or even the response from your audience. This makes your content more engaging.
- You can use the background for advertising. If your business uses live streaming to sell products or services, the background image is bonus real estate for displaying everything from product images to calls to action.
Green screening can also help increase the perceived value of your stream. It can allow you to do funny things, if you think you have a funny idea that can help you go viral. But it can also allow you to do serious things with presentations and charts. So it really does come down to helping you achieve your vision with the least expense possible.
What do you need to live stream with chroma key?
Let’s say you already have a live streaming setup that includes a camera and a computer with a software encoder installed. A camera is a camera, and the most widely used software encoders — OBS, XSplit, vMix— have some sort of background swapping functionality we can use.
In that case, the additions to your setup would include the actual green screen and, if you have the budget for it, additional lighting.
What kind of screen do you need?
Even though green is so associated with the process of chroma keying that “green screening” has become another name for it, the screen you use doesn’t necessarily have to be green.
The technique has been around for over a century. During that time, the color of the background screen changed a lot until we got the two variants we use today: green and blue. For a live streamer, it makes sense to use green for your background because:
- Green screens work better with digital cameras.
- They require less light than blue screens.
- There are reasons to believe that blue apparel is more popular than green, so there are fewer chances you’ll chroma key a clothing item.
Green isn’t without its faults, though, the biggest of which is that it bleeds over onto subjects, causing unintended chroma keying. One of the ways you can correct this bleed is with the use of lighting.
Either way, you shouldn’t have any trouble creating the screen. You can do anything from painting a wall with special paint to setting up a portable screen. Either will work fine, as long as it has consistent coloring.
What about lighting?
Lighting is where things become tricky and possibly expensive. It’s imperative that you light the green screen evenly. Any uneven coloration will make the screen more difficult to key. Plus, it will add more hues to the list of things you cannot wear in front of the green screen.
At the very least, you’ll need two lights with diffusers — one for each end of the screen. For a professional setup, it’s recommended that you add:
- Back light, to light the subject from the back and separate them from the background.
- Key light, the main light on the subject.
- Fill light, to fill in the shadows left from the key light.
That’s a lot of lights that probably require a lot of electricity. They might even produce a lot of heat. Prepare accordingly, and remember, with green screens, it’s all about lighting them evenly.
And computer hardware?
When you’re live streaming using a software encoder, you’re already putting the computer’s CPU under additional load. Chroma keying adds to that load, making the CPU work extra hard.
If your graphics card has it enabled, you can try switching to hardware encoding in OBS, and try to lighten the load that way. This will compromise the quality of your stream, however, and so will reducing the bitrate to help the CPU cope with the pressure.
Those are your best bets to chroma key a live stream on a subpar computer. It would be best to test your rig before the stream and think about upgrading to a new rig if your existing one cannot handle chroma keying.
How to set up the scene for your chroma-keyed live stream
So — there you are. You’ve checked your computer and determined it can handle the extra load. You’ve made the background as even and wrinkle-free as possible. You’ve got all the lighting you can afford, and you’re wondering what’s next.
Here are a couple of things for your pre-stream checklist you should take care of when setting up the stage for your green-screened live stream:
- Plan your shoot beforehand. This will help you determine the amount of screen you’ll need, plan the lighting and camera movements for dynamic shots, and generally give you a sense of control over the whole process. A little extra confidence won’t hurt you.
- Remove reflective or green items from the subject. Anything that’s green or that might reflect the color of the screen will be keyed out together with the background. Make sure the people in the video don’t wear anything that can cause an unwanted chroma key effect.
- Use a slightly bigger green screen than you think you’ll need. Just like that extra confidence, a larger green screen won’t hurt. But it just might prevent a disaster if something goes wrong with the framing. You don’t want the viewers to see what’s around the green screen.
- Have some distance between the subject and the screen. Obviously, you should do your best to avoid your subject casting shadows on the screen. Increasing the distance also helps with reducing the green light spill.
- Set and check the lighting with the subject in place. You want the screen to be of uniform brightness. Don’t light it too brightly, though, as this might cause bleeding and reflections. Pay close attention to any green you see on the subject — even blonde hair can reflect a green screen. Finally, you should light the subject as best as you can.
With that, you should have your scene set for the live stream. As you can see, it requires a bit more planning than your regular live stream. But as long as the end product is worth it, it shouldn’t be too big of a chore to set everything up.
Setting up chroma key in OBS (and most other encoders)
Let’s see how to use chroma keying with OBS Studio. The same steps would generally apply to almost any other software encoder.
- Set up everything as you would for a stream. Connect all the cables, plug everything in, and select your camera or capture device as the source in OBS.
- Add the visuals you want to key in. They also count as a source, so you can use everything from a video file to a slide show, a prepared image, or an animation file.
- Place it below your video source in the hierarchy. This tells OBS which are the original and which are keyed-in visuals.
- Add the chroma key effect filter. Right-click on your video source, find it on the list of available effect filters, and click on it to apply it.
- Fine-tune it. You’ll see chroma keying applied right away, and you’ll also have some options available for fine-tuning.
That’s it — you’re ready to stream. If you want to make sure your chroma-keyed video reaches the widest possible audience in an incredibly easy way, you should connect OBS Studio — or any other encoder you use — to a multistreaming tool. That way, you can spend more time setting up your chroma keying and working on your content than trying to get your audience to come to your channel.
Chroma keying is a great technique to use if you want to add some variety and creativity to your live stream. It doesn’t have to be expensive and too difficult to set up, although every bit of effort you put in will show in the final product.
It’s a popular technique, too — soon enough, you’ll be hard-pressed to find a streamer who doesn’t know how to use a green screen.
The same goes for multistreaming. Broadcasting to wherever your audience wants to see you is the perfect way to showcase the awesome things you’re doing with chroma keying. Don’t be the last to join the party — use Restream to broadcast your chroma-keyed streams to every corner of the world wide web!