Driving Large Displays From an iPad

Like any other application running on an iPad, the Kaon ADN Applications can be mirrored onto a large screen in a number of ways. The following information is not specific to our applications, but we are providing it to help our customers understand their options.

Remember that WiFi, particularly at a trade show, is unlikely to work when you most need it to. The WiFi network you are connecting to is likely to have insufficient bandwidth to carry video, and you may experience outages as you move about during a presentation.

Resolution & Aspect Ratio Issues

The iPad is a 4:3 aspect ratio device. All large monitors are 16:9 aspect ratio. That means that when you mirror the iPad, you will have black bars down the sides.

The monitor resolution is 1920x1080, whereas the iPad mirrored resolution is 1440x1080. So if you go with iPad mirroring, 25% of that 55” monitor’s width is going to be black bars (12.5% on each side).

The iPad cannot stream raw pixels at 1440x1080 at 60Hz, though. There isn’t enough bandwidth, even in the new lightning connector. So what they do is compress it to a very high quality H.264 feed at 30Hz, and then the cable itself decodes that video signal into raw HDMI pixels to send them to the screen.

So if you have a really large screen like a 55”, and you stand really close to it, you will see artifacts around text and along fine lines. If you step back a couple feet, you won’t be able to see these artifacts. And remember that since the iPad is the touch-input device in this scenario, there is no reason anyone would need to stand inches from that big screen!

The screen refresh rate will also be half when mirroring from the iPad, but the difference between 30Hz and 60Hz is not something most people would notice.

If your Kaon Application is available on the iPhone, that may be a better choice than an iPad. The iPhone 5 and later have a 16:9 aspect ratio, just like large monitors. So provided you hold it in landscape the whole time, the phone can fill the 1920x1080 screen. No black bars like you would have with an iPad.

The quality will be a little lower, though, because of the limitations of the Lightning connector. You are pushing 25% more pixels through, but the connector was already maxed out, so you will have to lose some quality. Again, you won’t be able to see these artifacts if you stand back a reasonable distance. It’s like the difference between a 95% quality JPEG and a 90% quality JPEG. Very subtle.

How to Connect

Wired HDMI will give the best signal by far. Although the signal does get compressed to get out the connector, it gets compressed a whole lot more for WiFi. So if reliability and image quality is your primary motivation, get an HDMI cable that is long enough to connect the monitor directly to the iPad.

If you want to send the image wirelessly, we have found the following procedure to be the most reliable approach.

Use a MacBook (or MacBook Air, or MacBook Pro) to connect the iPad to the big screen. Although you might be able to do this using a PC, staying in the Apple ecosystem is a much lower-risk way to go.

1. Install AirServer on the MacBook https://www.airserver.com pay for the business license ($20)

2. Connect the MacBook to the big screen using a cable. Be sure that you have the right cables for the MacBook you are using. Most MacBooks do not have HDMI ports, so you’ll need adapters (thunderbolt or USB-C, depending on the model).

3. On the Mac, go to the Apple menu (upper left corner) > About this Mac > System Report. Then choose WiFi from the left menu (under Network). This will give you a scan of all WiFi networks. Look at the channel of each WiFi network and see if you can find one that is not being used. If you don't see any network using 36, for example, then that's a great choice. The Mac will let you set up a network on channel 1, 6, 11, 36, 40, 44, or 48. If all those channels have activity, find the one with the lowest signal strength.

Remember that in the 2.4GHz range, channels 1, 6, and 11 are the only true channels. The ones between those borrow frequency from the ones above/below them. If you can keep line-of-sight between the Mac and the iPad, you will be much better off using a 5GHz channel (36, 40, 44, or 48).

4. From the WiFi menu choose Create Network… Choose the channel that you found to be least crowded.

5. On the iPad, connect the WiFi to that network you just created (it’ll appear below the other WiFi networks under “Devices”). It will warn you about not having an internet connection. That’s fine.

6. Make sure AirServer is running on the Mac, and start Screen Sharing from the iPad. It might take a few tries to get it going.

7. Once screen sharing is live, click the picture on the mac and make it full screen on the big display. (Remember that iPad is 4:3 aspect and your big display is probably 16:9 so some letterboxing is unavoidable.)