Different setup for OnTheAir CG (Internal, External Key vs Live Sources)

If you need to overlay dynamic graphics on top of video with OnTheAir CG, you will be able to choose between 2 different configurations:

  • using a video card that supports keying
  • using the "Live Sources" in OnTheAir CG

The great advantage of the "Live Sources" solution when used with OnTheAir Video or OnTheAir Node (and the direct link) is that you can have just one video output for both video and graphics, and you can use less expensive video cards.


1. Using a video card that supports Keying

There is an article in the knowledge base that lists the different cards that support keying. When looking at that article, make sure to check which one supports 

  • internal and/or external Keying
  • HD and /or SD Keying

Depending on what you want to do you will choose either internal or external keying.


Differences between Internal and External keying

With Internal keying, the keying is done by the video card itself. You enter the video signal in one of the input of the video card, and OnTheAir CG sends the graphics to be overlaid to the card that  overlays it on top of the incoming signal.

With External keying, the card will not mix the video and the graphics, the mix between the 2 will be done by an external device such as a Production Switcher.

When you enable the External Keying, the video card outputs 2 video signals using 2 connectors:

  • Fill = the actual graphics with colors and images
  • Key = a signal that tells the external device which portion of the image is transparent and which one is opaque. It is like an Alpha Channel.


So do you have to use Internal or External Key

It all depend on what you want to do. Of course the first thing to know is if you have (or want to purchase) an external keyer. There are some quite affordable ones, such as the ATEM from Blackmagic-Design.

External Key

There are 2 main advantages of using external key:

  • if the computer running OnTheAir CG is not running anymore, you'll still have a video signal. Indeed, when the external keyer don't receive signal from CG it will still show the video (unlike with internal key)
  • when used in a Live production, it's the director that decides when a graphic goes live or not on the production switcher.

Internal Key

The main advantage of internal key is the cost and simplicity... You don't have to purchase an additional device, support it and make sure you can use it. You just need to know that if you quit OnTheAir CG, the video signal will not be looped through and thus you need to be able to route your signal differently.


Used together with OnTheAir Video or OnTheAir Node

When you want to use OnTheAir CG together with OnTheAir Video or OnTheAir Node to overlay dynamic graphics, you can use a card that supports internal or external key, but it will mean then that you will need 2 video cards:

  • one video card that outputs video
  • one video card that overlays dynamic graphics on top of that video

This can work just fine (and has worked just fine in the past as it was the only way to do it), but it is more complex to setup as you need 2 video devices, and cable the video signals in between them. The advantage of that configuration is that the delay between the incoming video signal and when it is outputted is much shorter than with the "Live Sources"



2. Using Live Sources

Since OnTheAir CG 3.1 you can use "Live Sources" in OnTheAir CG. This is a great addition as it brings a lot of flexibility, because you can use video cards that don't support keying as well as use the direct link between OnTheAir Video (or OnTheAir Node) and OnTheAir CG.

As a quick reminder you can read the following article to understand what is the direct link in an example on how it is used with MovieRecorder: https://softron.zendesk.com/hc/en-us/articles/207694757-HOW-TO-Work-with-OnTheAir-Video-and-OnTheAir-Node-Direct-Link-

Here is how you should configure Live Sources in OnTheAir CG.


Playback preferences

In the playback preferences of OnTheAir CG, you can leave it to YUV, no need to enable ARGB.

Configure Live Sources

To create Live Sources, go to "OnTheAir CG > Preference > Live Sources". Then click on the + icon to create a new Live Source that you will be able to use in OnTheAir CG.

When you create a Live Source, you can set:

  • Live Source Name: is what will be displayed in the menu when you will create the Live item in OnTheAir CG Designer. Note that if you want to use the CG project in OnTheAir CG Server, you will have to use the exact same name in the preferences of OnTheAir CG Server. Only the name is important here, so make sure to configure the same name but you can use a different "source".
  • Video Device Input: this is where you select the Video Device to use (it can be a physical video input from a video device, or a direct link from OnTheAir Video or OnTheAir Node), and below that you set the other settings such as format and pixel format. You can use a different format than the one used for playback. If it is a different frame rate, we will duplicate or drop frames to maintain sync, and if it is a different size, we will scale it to match the output resolution.

You can create multiple Live Sources. For example here, I have created 2 Live Sources: one that uses the video input of an UltraStudio 4K and one that uses the direct link from OnTheAir Video.

Note that the Live sources are disabled by default, so you will have to enable them.

IMPORTANT!! It is recommended to genlock:

  • the device used to output with OnTheAir CG (the one set in the playback preferences)
  • the device that generates the video that is getting in the Live input (not the device used for the Live input, because you can not genlock inputs, only outputs can be genlocked). Indeed, if the video signal that gets in do not use the same clock as the device used by OnTheAir CG to playout, you may have frames being dropped and gear some audio drops


Add Live items to projects in OnTheAir CG Designer

Once the Live Sources are created, you can use them in your CG project. To add a Live source to a CG Project, click on the "L" icon in the toolbar:

As soon as you click on that icon, the Live item is created, will be entered in the middle of the screen using its real dimension. In the inspector, you can then change a few settings:

You can set:

  • the Live Source to use. In our example here, we have created 2 Live Sources, just select the one you want to use
  • Allow Smart Resize: you should enable that option if you use an interlaced source and you want to resize the sources to a different size than its natural size 
  • Invert field order: in case the field priority is wrong.

Once you have placed the Live item where you want to , just save the project so it is ready to be used in OnTheAir CG Server.


Using the projects in OnTheAir CG Server

Once the different projects are created, you can use them in OnTheAir CG Server. Note that you have to make sure to create the Live Sources using the same name in the preferences of OnTheAir CG Server.

Once you have configured the Live sources in the preferences, open the 2 Live projects.

Make sure also to sort the projects in the correct order. The project with the Live source should be placed at the bottom of  the list so the graphics are on top of it.



There can be 2 types of warnings on projects that hold Live items:

The attention sign means that the Live source uses a different fps than the playback settings configured for OnTheAir CG Server:


The red warning icon means that the Live Source is missing:


This can happen if:

  • the video device has been unplugged
  • OnTheAir Video (or OnTheAir Node) is not running
  • OnTheAir Video (or OnTheAir Node) did not play yet. Indeed the engine is only started when you start playing. So make sure to play something...


Important note about the delay

When using Live Sources in OnTheAir CG, you should know an important limitation: There will be a delay of more or less 12 frames (depends on the video card used) between the moment the signal gets in and the moment it is outputted. So it may not be suitable in some configurations. 



Have more questions? Submit a request