Video Signals to Projector for iOS4 Apps

What’s New

This is a fire-and-forget solution to mirroring the display of your iOS device (iPhone, iPod Touch, iPad) apps on an external display. It uses public APIs, so it can be used in apps published on the App Store. It supports detecting cabling (plugging and unplugging the display), orientation changes, and even offers a “tv safe mode” for displaying your app on an older analog video device.

How To Code

It's crazy easy. Just three steps:

1. Get the files AppProjector.m and AppProjector.h from this link and add them to your project.

2. In your app controller, add this to the other imports near the top: #import "AppProjector.h"

3. In your application's -applicationDidFinishLaunching: method, add this line: [[AppProjector sharedInstance] startTVOut];

Hardware Requirements

Since the launch of the iPad, Apple also offers a VGA connector cable, ostensibly iPad-only but which is what I used with an iPhone 4 while developing this code. I also tested with the composite out cable. Both cable seem to work fine. I’m not sure about iPhone 3GS and older devices, though — those devices may not support the VGA cable, although they certainly do support the composite and component cables.

While the TV output is running, if the video output cable is disconnected, the class will catch a notification, and stop sending video to the external window. Likewise, if a video output cable is connected, the class will catch that notification, and automatically start showing the video.

You don't even need to call -startTVOut -- just initialize the singleton sharedInstance, and the class will watch for cable connection notifications.

No Jailbreak API

This class uses app-store safe methods. You can ship apps that use this code. We are using an Apple-approvied safe-and-friendly method of collecting bitmaps of all visible windows, and then drawing that bitmap on the external screen, which is also displayed using Apple-approved non-private APIs.

Debugging with the Video Out Cable Attached

Obviously you can’t debug an app in Xcode without having the device connected via USB. Likewise, you can’t view the video output without having the VGA cable attached. So debugging was basically impossible.

Improvements Needed

Currently, device rotation is correctly tracked for the Portrait and Landscape Left initial starting positions. You can turn the device 90 degrees to the left or right and the view on the external monitor will rotate to match. (There’s even a nice animated rotation of the screen contents on the external video window.) However, portraitUpsideDown is not handled.

Compatibility Note

This class relies on certain APIs (i.e. [UIScreen screens]) that only exist in iOS SDK 3.2 and above.

AppProjector Class Reference

-sharedInstance
Creates a singleton instance (if it doesn’t already exist) and returns it. Starts listening to cable connection/disconnection and device orientation notifications.

-startTVOut
Creates a window on the second screen at the highest resolution it supports, and starts a timer (at the frames per second rate defined in the class file) to copy the screen contents to the window. If no screen is attached, -startTVOut will simply report a failure to the console.

-stopTVOut
Stops the periodic video-mirror timer (or thread) and releases the offscreen window.

tvSafeMode
When tvSafeMode is YES, the class will scale down the output size by 20%, so that the entire picture can fit within the visible scan area of an analog TV. If you don’t know what an analog TV is, don’t worry, you’ll probably never see one.