Hello. I am all of a sudden having this same problem on iOS through Unity. I have been all over the forums here and have seen that lots of folks are having this issue. I've tried a few different things that have been posted here but have had no luck getting this to work again.
Here is the information about my hardware and software that I'm using and what's going on:
iPhone 6 plus - 8.1.3
ipad air 2 - 8.1.2
I have an ongoing public facing project for a client that has been available in the iOS app store and in Google Play for almost 2 years. We've been updating it and supporting it regularly since its initial release. It has been well received by their customers and our hope is to push out this update and go into high gear with promoting it.
I migrated the project to Vuforia 3.0.9 (after backing up as I always do) about a month ago and things still worked fine. The only changes that have been made to the project in the last month have been to the main menu UI and not the AR viewer portion of the app. I did Update Unity to 4.6.3f1 but I was already using 4.6 prior to this problem with no issues.
If I set the Graphics API level in Unity to Automatic, the iOS build runs with the infamous black screen. My UI shows up over top of it but no video from the camera. I have gone into settings on each device and made sure that camera is allowed for my app. (I've even toggled it on and off to see if it would kick things on. No luck.) Stranger still, if I point my device (all in black) at one of my markers, the augment shows up over black. So I believe Qcar and the device camera are working.
I am well aware of the UISupportedInterfaceOrientations crash bug in Vuforia 3.0.9 and I know how to fix it quickly. That is not the issue. (See liwei1dao's post at this thread: http://forum.unity3d.com/threads/unity-4-6-0b20-vuforia-3-0-9-ios-exc_bad_access.274387/)
I have also attempted AlessandroB's fix for the current problem posted here: https://developer.vuforia.com/forum/device-support/black-screen-ios-devices-camera-mode and that also did not work. Again, the augments in my project do appear over black when my device's camera is pointed at the markers so I firmly believe that the camera is indeed working.
When the Graphics API level is set to Open GL ES 2.0 or 3.0 I see the camera feed but only in the bottom left hand corner.
The app does not crash while running when not tethered to Xcode, just no video feed from the camera. However, when in Xcode, it will throw up an EXC_BAD_ACCESS. I've attached a screenshot.(when set to API-auto)
I have made all of my client's most recent revisions and this latest update is now completely done and ready to be published. A lot of work has gone into this project in the last month and I would very much like to see it published (as would my client!) This screen problem is now holding everything up.
I know that ultimately this project will need to migrate to 4.0 but I would very much like to push this one out with 3.0.9 for now. Cloud reco is not an option for this project.
Everything has ground to a complete standstill at this point. Any help is greatly appreciated!!