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Use your iDevice as an extra display for your Mac (duetdisplay.com)
182 points by bauerpl on Dec 15, 2014 | hide | past | favorite | 112 comments

I wonder how they achieve "Zero lag". I've been using similar software ( AirDisplay [1] ) and the lagging is awful.

You have to be certified hardware manufacturer if you want to use the USB connection to transmit any data between the iPad and your Mac [2]. So my bet is they either use WiFi ( which can roughly get 60fps on retina resolution ) or Bluetooth 4. In both cases I think the refresh rate would not satisfy in a lot of cases, e.g. playing a YouTube video through their software on the iPad.

1: https://avatron.com/applications/air-display/ 2: https://avatron.com/support/faq-air-display/#toggle-id-13


I've found more information on their facebook page [3]

> To setup, download and open duet on your Mac (for free) and on iOS.

> Connect your device using a lightning or 30 pin cable. Done.

> No need to worry about firewall settings, Wi-Fi speed or your 802.11n network.

> Duet is secure, simple, and allows you to use your iOS and OS X devices in harmony.

So I guess I was wrong with my bets. Maybe they got a hardware manufacturer license from Apple. Anyway launch is on 16th, so let's see.

3: https://www.facebook.com/duetdisplay/info?tab=page_info

"Most importantly, Duet Display is the first app that actually turns your iPad into a second display I’d actually like to use. As someone who has tried Air Display and uninstalled it shortly afterward, frustrated, I can honestly say this is the only option that’s worth it."

Interesting, I tried Air Display and (another app) ages ago and used it off and on. It was "neat" and worked well as my Terminal window but a very poor stand for a monitor.

Looks like I'll be dusting off my iPad 2.

My guess would be they're just using the shared documents area .

There's a number of libraries on the desktop that let you access an API to write to the shared documents area. I'd guess they'd just be piping a mp4 feed to this and the iOS would just be reading from there.

> [...] shared documents area. I'd guess they'd just be piping a mp4 feed to this [...]

If this is the case I'd worry about the internal flash drive of the iPad. There must be a lot writes.

Is there any chance this approach could eventually be used on a Linux distro or Windows?

The technology already exists in X11. The problem is getting devices to act as display servers.

I haven't seen examples of folks trying to use iPads (for example) as X11 displays, likely because it's outside my area of expertise. Do you know of any examples?

iSSH includes an X11 display server, and I've had reasonable success using it with clients on an assortment of architectures, including a Tru64 VM running Open Genera. I wouldn't expect it to work well with something like video playback unless you've got a very fast and uncongested wireless network (or possibly a Lightning-to-Ethernet adapter, if such things exist), but if you don't need that kind of sustained responsiveness, it's at least worth a try.

I think the original product link isn't using wireless but instead depends on a wired connection. I've heard about using X11 over the internet but I'm worried that the lag would make this approach more annoying than effective.

It would be great to have a wired connection option on other operating systems besides the Mac.

Sounds like something that could only exist on Cydia. Has anyone checked there?

I do a lot of reading / annotating on my iPad. My other use case mostly involves emacs. I'd love to have a Linux matchstick dongle that I could simply plug in to my iPad to run emacs (and associated goodies like R, Python, etc).

There's a working download link in the footer, not sure why.

I downloaded the application, and it prompted a restart to install a driver, but did nothing further. duet.app does nothing when I open it, and plugging in my iPad does nothing either. Looks like we have to wait for the App Store release to install the iPad half of the app.

After installing, there is an icon in my menubar that says I should open duet on my iOS [1]. I believe we wait for the iOS app tomorrow and see what's the price and how this thing works

1: http://i.imgur.com/1fEHPLF.png

I've been beta testing duet for about a month now. As a person that travels a lot, it's awesome. The developers have done an incredible job, and have been very responsive in fixing the bugs I've reported to them.

However, a couple of things to note. Firstly, this is lag free, but still not something you should play videos on. I'm not sure what the framerate is, but I'd be surprised if it's over 30fps. I believe this is probably a result of using USB.

Secondly, I never thought I'd say this, but retina is not your friend. On the new iPads, the OS X menu bar is maybe a centimeter tall. Obviously, you can change the resolution, but I like hi-res, and you just see so little when you bump it up (keep in mind the new iPad is only 1024 by 768).

The app is the best it can be, but what I'd emphasize is that most people should really get a second monitor, if that's what they're looking for. I understand you could save some money, but iPads just don't offer enough real estate.

Again, kudos to the devs for doing a great job on the app though.

They claim 60fps with no lag.

That figure could refer to "typical" usage, where most of the screen doesn't have to update.

This app would be pretty useful when the new bigger iPad comes out.

This isn't the first app that lets you do this, is it? It might be better (or worse) in performance, but the functionality has already been made available in the past, right? Just want to check.

Also, this is neat but I wish it were integrated into OS X + iOS as part of AirPlay. I love AirPlay and want to see it expand to cover all possible permutations (iOS -> OS X screen/audio/both sharing, as well as OS X -> iOS screen/audio/both sharing). That would go well under the Continuity moniker and is something Apple can do well thanks to their control.

Hopefully it's one of the minor new features in next Apple OS updates.

I've used an app called Air Display to do the same thing for quite a while, but instead of USB it connects over WiFi - which is convenient, but the refresh rate is slow. I used it mainly to have my chat client on a 3rd screen.

This is really interesting technically, a couple tidbits I dug up looking in the mac app bundle:

1. There are a couple of OpenGL shaders in the bundle for converting the screen image to HDTV color space/format (420v.fgsh) and some kind of passthrough.

2. They appear to be using x264 to encode the screen with defaults of 1280x720, 1000kbit, superfast preset. (Defaults.plist)

So on the mac side, they're definitely capturing the screen and sending a streaming video. Not surprising, but the curious part is how they manage to get the iPad to stream in that data over USB. I suppose something like HTTP Live Streaming[1] could work. Place small files into the device's Documents area, and they get streamed. It would be awesome if something else was going on here - like a named pipe.

1. https://developer.apple.com/streaming/

My guess is it's using Apple's version of RNDIS ... iPad becomes a network peer of the Mac and streams video over that network.

But I don't believe that API is public, so I can't know for sure...

I know this is nit-picky, but Duet is not "the first app that allows you to use your iDevice as an extra display". It's not even the second. There's an opportunity here for better copy to differentiate themselves.

Also, I've always thought this would reduce the life of your ipad. Has anyone noticed this?

you chopped off this part "...iDevice as an extra display for your Mac using the Lightning or 30-pin cable"

How? Like the display burning out or something? Maybe something battery related?

Battery is definitely a concern, though it probably doesn't matter since it will be plugged up. The screen dimming might be a concern for me as well. Honestly though, now that I think about it, I've never been worried about that with my laptop, so I probably shouldn't care about it with my ipad.

Best part of this: "All iPads."

My iPad 1 is pretty much a paperweight these days (I know, I know, never buy the first version of anything Apple). This could be a great new use for it.

Seriously. I was going to give away my first gen ipad but due to being so outdated it seemed more of an imposition than a gift.

What's wrong with it? I have a first gen iPad and it still works fine. In fact I almost wish it would die already so that I would have a valid excuse to buy a new one.

Did you upgrade iOS to version 5? I did, and it's never been the same since. I can now barely use the web browser without it crashing. Some domains are totally unusable; appears to be related to javascript use. Low-impact sites, such as HN, are OK. Other apps (such as the app store and many games) are very prone to crashing, too. There's very little I can use it for now without getting frustrated and giving up.

I have the same experience. I wish I could get a better web browser for it. my ipad 1 is just a video player/ book reader at this point (which isn't bad, just not grat)

I just checked, and I'm running 5.1.1. No crashes, no problems worth mentioning. Sure it's not the fastest thing on the block, but most sites and apps I use run perfectly fine. Admittedly I don't really play any CPU or graphics intensive games.

Most kids games won't run on it.

Mine is full of kids games. Admittedly I've run across one or two games that didn't work, but it's not like I've ever experienced a lack of available kids games.

Thanks, I will have to try it again.

> the first app that allows you to use your iDevice as an extra display for your Mac

I stumbled upon iDisplay.com the other day. Can't recommend anything though, I'm not an apple user, I was looking for ways to replicate my android phone display in my desktop Linux.

Did you find anything worth using for your use case?

Not really: I tried android-screencast [1] but had to root my phone, the framerate was terrible, lots of crashes, touch gestures not really satisfying.

The other option was using genymotion, works well, but some apps can't be installed multiple times (whatsapp I'm looking at you).

If anyone knows a better way to do so, thank you in advance!

[1] https://code.google.com/p/androidscreencast/

http://web.airdroid.com/ maybe? Lots of drawbacks, though, and not 1:1 mirroring I believe, so may not fit your needs. But seems to support whatsapp via screen mirroring + custom keyboard (probably?). Haven't tested since I'm currently on iOS.

Koush's Mirror app[1] works alright with his Allcast Receiver Chrome app. The interesting thing is that using it actually revealed a (broken) second screen mode in one of the apps I use, didn't know Android had APIs for that. Perhaps it's intended for Chromecast/Miracast and whatever Mirror does looks like that.

[1] https://play.google.com/store/apps/details?id=com.koushikdut...

For a little bit I was using a Nexus 10 as a secondary display - I used Google Chrome's remote desktop to view a separate X session, with Synergy for sharing my input devices between them (which is now paid for?!). Worked great, except you couldn't see the mouse cursor on the Nexus... :( Ultimately it was more annoying than helpful. (Edit: just realised that's broadcasting in the opposite direction to what you're asking for)

Yeah, that statement is purely false. AirDisplay[1] does pretty much the same thing and has been out for years.

[1]: https://avatron.com/applications/air-display/

the commenter misquoted, the rest of the sentence is "... iDevice as an extra display for your Mac using the Lightning or 30-pin cable."

Here's the bit I was looking for: http://www.duetdisplay.com/#compatibility

Compatible with all iPads, nice! I have an old iPad 1 lying around that runs very few of the apps I would like to use with it (Office suite and VLC, mostly), so I've been looking for a way to repurpose it, and this might be it.

Looks like they changed it to "All iPad hardware with iOS 6 and above". Which means no iPad 1. :(

OK Guys After I installed and launched this MacOS app , it drastically slowed down my chrome and increased the chrome cpu usage. I am guessing something wrong with the duet app display driver.

so if anyone having the same problem like mine, please go to finder, search for "duetdisplay.kext" kernal extension, delete it and reboot your Mac. It should go back to normal.

If it is really real-time this will be interesting. In combination with SideCar you could have a nice mobile dual-screen setup.


The iAccessories pictured looks really beautiful. Anyone know what brand it is?

Amusingly, these are sold by Evernote: https://www.evernote.com/market/feature/pfeiffer

If you like these you may also like Grovemade - http://grovemade.com. Initially I even thought it was from them.

If you want a proper external monitor to go with your laptop, invest in something like this: http://www.bhphotovideo.com/c/product/1021217-REG/asus_mb168....

+1 for linking to the lowest price I can find for it on the web (199 vs Amazon's 266).

Well, the app is obviously working for some folks, but in my case it's junk. 13" MBA 2012 OS X 10.10.1 connecting with iPad Mini Retina or iPhone 5s (both iOS 8.1.2) using genuine Apple Lightning cable and direction connection (i.e. no USB hub). Most of the time the iOS app never gets beyond the "Connect to Mac" stage, even though the screen flashes on the Mac indicating new display hardware is available. Sometimes the iOS app gets to the "Launching Duet…" and hangs. Rarely, the iOS app actually becomes a display; however, when that happens my mouse is frozen (in a "stuttering" sort of way). Waste of good money for me.

I have been testing this as well; it is really great for travelling. I put my air 2 on high res and find myself hardly using my normal screen anymore. There are a few bugs but those will be gone soon I reckon; the creators respond fast to mail.

Duet is the first app that allows you to use your iDevice as an extra display for your Mac.

What am I missing about this sentence that seems to make "the first" false in the face of things like Air Display?

It's tethered using lightning cable.

Wrong. I have been using my iPad as an extra display for my MacBook Air for about 2 1/2 years using the AirDisplay (getairdisplay.com).

It is odd that this company would place a large lie as the first readable text.

You did not read the whole sentence.

Duet is the first app that allows you to use your iDevice as an extra display for your Mac using the Lightning or 30-pin cable.

This app uses a cable. All the other apps use wifi.

They have obviously changed the copy in the last few hours. The second half of that sentence ("Using…") was not there earlier.

I'm happy this application made its way onto Hacker News. First heard it from a founding team member and thought the use-case is immense.

I've occasionally used AirDisplay when doing minor HTML/CSS stuff (browser on iPad, emacs with impatient-mode on Mac) and it's useful, nice, but when doing heavier lifting lag kills it. I'll definitely be getting it tomorrow, and look forward seeing if I get to use it more or "as often as I did."

It would be neat if they could figure out a way to let you use an iMac screen as a secondary monitor for a mbp.

Plug a Mini DisplayPort cable into both machines, hit Cmd+F2 (as far as I recall) on the MBP.

This is already built-in: http://support.apple.com/kb/PH14264

Woah, do you know if this works with the new retina display iMacs?

No, sorry to disappoint you!


At the risk of answering without a guaranteed answer, "probably not," given the amount of the power necessary to drive that screen and complex architecture inside the box to make it work. But Target Display Mode as a thing has been around for a while.

I'm here to confirm to you that it doesn't. Sorry buddy, wish it did myself. 5K is out of reach for most MBP's (if not all).

That's a bummer, it would be worth buying a new iMac for the screen alone.

I've been using Air Display for a long time for when I'm on the go. Does anybody have experience with both and which is better? Never really had problems with Air Display - if you don't expect it to work as a full external display. However lag has always been very manageable for me

Product launches tomorrow, so hardly any comparisons can be made. It seems to be promising - wired connection means higher bandwidth and improved latency. Supposedly can do Retina resolutions at 60hz.

I see now, I should have been reading better - my bad. I also read in this thread that Air Display had some troubles with Yosemite, but I haven't updated on my work machine yet so I hadn't seen these problems.

Streaming over USB seems promising though, I needed to plug in my iPad for the battery.

So uh, why is the marketing being done today when the release is tomorrow? I'll probably have forgotten about it by then. I wouldn't mind it though, the other ones (using wifi streaming) never really worked for me. And I wonder why this isn't a default feature in iOS / OSX.

So uh, why is the marketing being done today when the release is tomorrow?

They want your email, Twitter following, and other things that are more useful over time than your casual perusal after launch.

Actually a bit simpler, Business Insider released the article to fill their timeline not Duet's launch date. The app is still awaiting review and with the app store being so busy this season it's hard to give a hard date. Expected to be released later this week.

I've actually just downloaded their MacOS App and tried to install and launch it.

It now basically does nothing just blinking in the statues bar.

But I observe sudden CPU usage surge of this app from the activity monitor, not sure whether it is because of not pairing an iOS app or not

And also, my chrome feels significantly lagged.

mhm in my case once I opened the App it just disappeared. It moved itself to the Application directory, can't say I like this.

will it slow something down?

I would love to use this to share my Macbook screen on an iPad with a client. One screen seems to small for more than two people to share. Perhaps I could even connect multiple iPads for small presentations without a projector. All running in mirror mode.

Anything like this available for Windows? Wouldn't be bad for an email/IM screen.

Any VNC app allows you to view and control your screen. I like RealVNC. The corresponding app on Android and iOS is called VNC Viewer. There are several companies/projects that offer this functionality.

I meant adding the iPad as an additional screen (with additional desktop space) for a Windows machine.

The line "An additional display increases productivity by up to 48%." is particularily funny.

I wonder how they "measured" this. A Macbook Air 11" + extra display is quite different from a Macbook Pro 15" + extra display.

"up to".

So where is it?!? It's the 16th and nowhere to be seen. BusinessInsider.com is now saying the 17th. I also wonder why they removed the Mac app from duetdisplay.com.

Wonder how much bandwidth is required to drive this... My USB3.0 port is taken by an SSD hosting virtual machines, the other is hooked to a powered hub.

Assuming the video stream is compressed (MP4?) it shouldn't take too much. We're pretty used to streaming HD over the internet, so even USB2 should be able to handle it.

I signed up for the newsletter and the download button appeared but it just hangs there and I can't download the app. How do I download the app?

This looks cool - I'd definitely use it for emails. Has it not been done already though?

I have a question about the image - whats the stand used for the iPad?

Regarding it being done before, I tried this app (http://minidisplayapp.com/userguide/en/) that offered similar with an iPad mini, but the extra space wasn't really big enough to make it worthwhile.


12 south are pretty nice, but my wife had a bad experience with their SurfacePad iPhone case (really awesome case, but the leather wears heavily after 1-2 months)

Isn't the point of leather that it wears?

Am I a little too slow here or they just launched the Mac app without the iOS counterpart? Can't find it on App Store.

The CTA at the end is to sign up for a launch email so I guess it's not ready yet.

You're too fast, the release date for the iOS app is 16th december.

Ah. I see. Got a little confused because the Mac app is already available, so I thought it was just a matter of old sign up form not removed from site yet.

Duet is still waiting in line for approval in the app store. Launch is later this week.

I'd really like this to work with my old iMac G5. It has a great monitor, but I struggle to find uses for it.

Do I need an iDevice to view the video as well? Wont play here, would be interested to see more how this works.

You don't need an iOS device to watch the website's ad. It's an embedded YouTube video. Here's the direct link: https://www.youtube.com/watch?v=mVYimOiEya8

Finally, something to do with my 1st generation iPad.

You could have used Air Display :) I do really like this use though, never thought of using my old iPad as a permanent extra display.

Fantastic! Been wanting this for, like, ever

is it out yet?

It is called AirDisplay and available since years: https://avatron.com/applications/air-display/

I think there was/is also another App available doing it.

...and then yosemite came out, the the fps dropped from 25 to 2, and everyone stopped using it.

The same goes for DisplayPad.

The key here is that this is not a wifi streamcast.

There are plenty of apps which have done this before - but only over Wifi. This is wired, so you don't get the same issues with lag.

I've used Air Display, but that's over Wifi.

These guys claim to be using the lightning cable. Which means maybe, just maybe, I can plug two of them in at once.

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