Jelly Bean

Welcome to Android 4.2, the latest version of Jelly Bean!

Android 4.2 has performance optimizations, a refreshed system UI, and great new features for users and developers. This document provides a glimpse of what's new for developers.

See the Android 4.2 APIs document for a detailed look at the new developer APIs.

Find out more about the new Jelly Bean features for users at www.android.com.

Faster, Smoother, More Responsive

Android 4.2 builds on the performance improvements already included in Jelly Bean — vsync timing, triple buffering, reduced touch latency, and CPU input boost — and adds new optimizations that make Android even faster.

Improvements in the hardware-accelerated 2D renderer make common animations such as scrolling and swiping smoother and faster. In particular, drawing is optimized for layers, clipping and certain shapes (rounded rects, circles and ovals).

A variety of WebView rendering optimizations make scrolling of web pages smoother and free from jitter and lags.

Android’s Renderscript Compute is the first computation platform ported to run directly on a mobile device GPU. It automatically takes advantage of GPU computation resources whenever possible, dramatically improving performance for graphics and image processing. Any app using Renderscript on a supported device can benefit immediately from this GPU integration without recompiling.

Refined, refreshed UI

Android 4.2 refines the Jelly Bean user experience and brings familiar Android UI patterns such as status bar, system bar, and notifications window to all tablets.

All screen sizes now feature the status bar on top, with pull-down access to notifications and a new Quick Settings menu. The familiar system bar appears on the bottom, with buttons easily accessible from either hand. The Application Tray is also available on all screen sizes.

One tablet, many users

Now several users can share a single Android tablet, with each user having convenient access to a dedicated user space. Users can switch to their spaces with a single touch from the lock screen.

On a multiuser device, Android gives each user a separate environment, including user-specific emulated SD card storage. Users also have their own homescreens, widgets, accounts, settings, files, and apps, and the system keeps these separate. All users share core system services, but the system ensures that each user's applications and data remain isolated. In effect, each of the multiple users has his or her own Android device.

Users can install and uninstall apps at any time in their own environments. To save storage space, Google Play downloads an APK only if it's not already installed by another user on the device. If the app is already installed, Google Play records the new user's installation in the usual way but doesn't download another copy of the app. Multiple users can run the same copy of an APK because the system creates a new instance for each user, including a user-specific data directory.

For developers, multi-user support is transparent — your apps do not need to do anything special to run normally in a multi-user environment and there are no changes you need to make in your existing or published APKs. The system manages your app in each user space just as it does in a single-user environment.

New ways to engage users

Lock screen widgets

In Android 4.2, users can place app widgets directly on their lock screens, for instant access to favorite app content without having to unlock. Users can add as many as five lock screen widgets, choosing from widgets provided by installed apps. The lock screen displays each widget in its own panel, letting users swipe left and right to view different panels and their widgets.

Like all app widgets, lock screen widgets can display any kind of content and they can accept direct user interaction. They can be entirely self-contained, such as a widget that offers controls to play music, or they can let users jump straight to an Activity in your app, after unlocking along the way as needed.

For developers, lock screen widgets offer a great new way to engage users. They let you put your content in front of users in a location they’ll see often, and they give you more opportunities to bring users directly into your app.

You can take advantage of this new capability by building a new app widget or by extending an existing home screen widget. If your app already includes home screen widgets, you can extend them to the lock screen with minimal change. To give users an optimal experience, you can update the widget to use the full lock screen area when available and resize when needed on smaller screens. You can also add features to your widgets that might be especially useful or convenient on the lock screen.

Daydream

Daydream is an interactive screensaver mode that starts when a user’s device is docked or charging. In this mode, the system launches a daydream — a remote content service provided by an installed app — as the device screensaver. A user can enable Daydream from the Settings app and then choose the daydream to display.

Daydreams combine the best capabilities of live wallpapers and home screen widgets, but they are more powerful. They let you offer the any kind of content in a completely new context, with user interactions such as flipping through photos, playing audio or video, or jumping straight into your app with a single touch.

Because daydreams can start automatically when a device is charging or docked, they also give your app a great way to support new types of user experiences, such as leanback or exhibition mode, demo or kiosk mode, and "attract mode" — all without requiring special hardware.

Daydreams are similar to Activities and can do anything that Activity can do — from rendering a UI hierarchy (without using RemoteViews) to drawing directly using Canvas, OpenGL, SurfaceTexture, and more. They can play video and audio and they can even accept direct user interaction. However, daydreams are not Activities, so they don’t affect the backstack or appear in Recents and they cannot be launched directly from your app.

Implementing a daydream is straightforward and you can take advantage of UI components and resources that you’ve already created for other parts of your app. You can provide multiple daydreams in your app and you can offer distinct content and display settings for each.

External display support

Android 4.2 introduces platform support for external displays that goes far beyond mirroring — apps can now target unique content to any one or multiple displays that are attached to an Android device. Apps can build on this to deliver new kinds of interaction and entertainment experiences to users.

Display manager

Apps interact with displays through a new display manager system service. Your app can enumerate the displays and check the capabilities of each, including size, density, display name, ID, support for secure video, and more. Your app can also receive callbacks when displays are added or removed or when their capabilities change, to better manage your content on external displays.

Presentation window

To make it easy to show content on an external display, the framework provides a new UI object called a Presentation — a type of dialog that represents a window for your app’s content on a specific external display. Your app just gives the display to use, a theme for the window, and any unique content to show. The Presentation handles inflating resources and rendering your content according to the characteristics of the targeted display.

A Presentation gives your app full control over the remote display window and its content and lets you manage it based on user input events such as key presses, gestures, motion events, and more. You can use all of the normal tools to create a UI and render content in the Presentation, from building an arbitrary view hierarchy to using SurfaceView or SurfaceTexture to draw directly into the window for streamed content or camera previews.

Preferred display selection

When multiple external displays are available, you can create as many Presentations as you need, with each one showing unique content on a specific display. In many cases, you might only want to show your content on a single external display — but always on the that’s best for Presentation content. For this, the system can help your app choose the best display to use.

To find the best display to use, your app can query the display manager for the system’s preferred Presentation display and receive callbacks when that display changes. Alternatively, you can use the media router service, extended in Android 4.2, to receive notifications when a system video route changes. Your app can display content by default in the main Activity until a preferred Presentation display is attached, at which time it can automatically switch to Presentation content on the preferred display. Your apps can also use media router’s MediaRouteActionProvider and MediaRouteButton to offer standard display-selection UI.

Protected content

For apps that handle protected or encrypted content, the display API now reports the secure video capabilities of attached displays. Your app query a display to find out if it offers a secure video output or provides protected graphics buffers and then choose the appropriate content stream or decoding to make the content viewable. For additional security on SurfaceView objects, your app can set a secure flag to indicate that the contents should never appear in screenshots or on a non-secure display output, even when mirrored.

Wireless display

Starting in Android 4.2, users on supported devices can connect to an external display over Wi-Fi, using Miracast, a peer-to-peer wireless display standard created by the Wi-Fi Alliance. When a wireless display is connected, users can stream any type of content to the big screen, including photos, games, maps, and more.

Apps can take advantage of wireless displays in the same way as they do other external displays and no extra work is needed. The system manages the network connection and streams your Presentation or other app content to the wireless display as needed.

Native RTL support

Android 4.2 introduces full native support for RTL (right-to-left) layouts, including layout mirroring. With native RTL support, you can deliver the same great app experience to all of your users, whether their language uses a script that reads right-to-left or one that reads left-to-right.

When the user switches the system language to a right-to-left script, the system now provides automatic mirroring of app UI layouts and all view widgets, in addition to bidi mirroring of text elements for both reading and character input.

Your app can take advantage of RTL layout mirroring in your app with minimal effort. If you want the app to be mirrored, you simply declare a new attribute in your app manifest and change all "left/right" layout properties to new "start/end" equivalents. The system then handles the mirroring and display of your UI as appropriate.

For precise control over your app UI, Android 4.2 includes new APIs that let you manage layout direction, text direction, text alignment, gravity, and locale direction in View components. You can even create custom versions of layout, drawables, and other resources for display when a right-to-left script is in use.

To help you debug and optimize your custom right-to-left layouts, the HierarchyViewer tool now lets you see start/end properties, layout direction, text direction, and text alignment for all the Views in the hierarchy,

Enhancements for international languages

Android 4.2 includes a variety of font and character optimizations for international users:

• For Korean users, a new font choice is available — Nanum (나눔글꼴) Gothic, a unicode font designed especially for the Korean-language script.
• Improved support for Japanese vertical text displayed in WebViews.
• Improved font kerning and positioning for Indic, Thai, Arabic, and Hebrew default fonts.

The default Android keyboard also includes an updated set of dictionaries:

• Improved dictionaries for French (with bigram support), English, and Russian
• New dictionaries for Danish, Greek, Finnish, Lithuanian, Latvian, Polish, Slovenian, Serbian, Swedish, Turkish

New ways to create beautiful UI

Nested Fragments

For more control over your UI components and to make them more modular, Android 4.2 lets you nest Fragments inside of Fragments. For any Fragment, a new Fragment manager lets you insert other Fragments as child nodes in the View hierarchy.

You can use nested Fragments in a variety of ways, but they are especially useful for implementing dynamic and reusable UI components inside of a UI component that is itself dynamic and reusable. For example, if you use ViewPager to create fragments that swipe left and right, you can now insert fragments into each Fragment of the view pager.

To let you take advantage of nested Fragments more broadly in your app, this capability is added to the latest version of the Android Support Library.

Accessibility

The system now helps accessibility services distinguish between touch exploration and accessibility gestures while in touch-exploration mode. When a user touches the screen, the system notifies the service that a generic touch interaction has started. It then tracks the speed of the touch interaction and determines whether it is a touch exploration (slow) or accessibility gesture (fast) and notifies the service. When the touch interaction ends, the system notifies the service.

The system provides a new global accessibility option that lets an accessibility service open the Quick Settings menu based on an action by the user. Also added in Android 4.2 is a new accessibility feedback type for Braille devices.

To give accessibility services insight into the meaning of Views for accessibility purposes, the framework provides new APIs for associating a View as the label for another View. The label for each View is available to accessibility services through AccessibilityNodeInfo.

Improved Camera with HDR

Android 4.2 introduces a new camera hardware interface and pipeline for improved performance. On supported devices, apps can use a new HDR camera scene mode to capture an image using high dynamic range imaging techniques.

Additionally, the framework now provides an API to let apps check whether the camera shutter sound can be disabled. Apps can then let the user disable the sound or choose an alternative sound in place of the standard shutter sound, which is recommended.

Renderscript Computation

In Android 4.2, Renderscript Compute introduces new scripting features, new optimizations, and direct GPU integration for the highest performance in computation operations.

Filterscript

Filterscript is a subset of Renderscript that is focused on optimized image processing across a broad range of device chipsets. Developers can write their image processing operations in Filterscript using the standard Renderscript runtime API, but within stricter constraints that ensure wider compatibility and improved optimization across CPUs, GPUs, and DSPs.

Filterscript is ideal for hardware-accelerating simple image-processing and computation operations such as those that might be written for OpenGL ES fragment shaders. Because it places a relaxed set of constraints on hardware, your operations are optimized and accelerated on more types of device chipsets. Any app targeting API level 17 or higher can make use of Filterscript.

Script intrinsics

In Android 4.2, Renderscript adds support for a set of script intrinsics — pre-implemented filtering primitives that are accelerated to reduce the amount of code that you need to write and to ensure that your app gets the maximum performance gain possible.

Intrinsics are available for blends, blur, color matrix, 3x3 and 5x5 convolve, per-channel lookup table, and converting an Android YUV buffer to RGB.

Script groups

You can now create groups of Renderscript scripts and execute them all with a single call as though they were part of a single script. This allows Renderscript to optimize execution of the scripts in ways that it could not do if the scripts were executed individually.

If you have a directed acyclic graph of Renderscript operations to run, you can use a builder class to create a script group defining the operations. At execution time, Renderscript optimizes the run order and the connections between these operations for best performance.

Ongoing optimization improvements

When you use Renderscript for computation operations, you apps benefit from ongoing performance and optimization improvements in the Renderscript engine itself, without any impact on your app code or any need for recompilation.

As optimization improves, your operations execute faster and on more chipsets, without any work on your part. The chart at right highlights the performance gain delivered by ongoing Renderscript optimization improvements across successive versions of the Android platform.

GPU Compute

Renderscript Compute is the first computation platform ported to run directly on a mobile device GPU. It now automatically takes advantage of GPU computation resources whenver possible to improve performance. With GPU integration, even the most complex computations for graphics or image processing can execute with dramatically improved performance.

Any app using Renderscript on a supported device can benefit immediately from this GPU integration, without recompiling. The Nexus 10 tablet is the first device to support this integration.

New built-in developer options

The Android 4.2 system includes a variety of new developer options that make it easier to create great looking apps that perform well. The new options expose features for debugging and profiling your app from any device or emulator.

On devices running Android 4.2, developer options are hidden by default, helping to create a better experience for users. You can reveal the developer options at any time by tapping 7 times on Settings > About phone > Build number on any compatible Android device.

New developer options in Android 4.2 include:

• Take bug report — immediately takes a screen shot and dumps device state information to local file storage, then attaches them to a new outgoing email message.
• Power menu bug reports — Adds a new option to the device power menu and quick settings to take a bug report (see above).
• Verify apps over usb — Allows you to disable app checks for sideloading apps over USB, while still checking apps from other sources like the browser. This can speed up the development process while keeping the security feature enabled.
• Show hardware layers updates — Flashes hardware layers green when they update.
• Show GPU overdraw — Highlights GPU overdraw areas.
• Force 4x MSAA — Enables 4x MSAA in Open GL ES 2.0 apps.
• Simulate secondary displays — Creates one or more non-secure overlay windows on the current screen for use as a simulated remote display. You can control the simulated display’s size and density.
• Enable OpenGL traces — Lets you trace OpenGL execution using Logcat, Systrace, or callstack on glGetError.

New Platform Technologies

Android 4.2 includes a variety of new and enhanced platform technologies to support innovative communications use-cases across a broad range of hardware devices. In most cases, the new platform technologies and enhancements do not directly affect your apps, so you can benefit from them without any modification.

Security enhancements

Every Android release includes dozens of security enhancements to protect users. Here are some of the enhancements in Android 4.2:

• Application verification — Users can choose to enable “Verify Apps" and have applications screened by an application verifier, prior to installation. App verification can alert the user if they try to install an app that might be harmful; if an application is especially bad, it can block installation.
• More control of premium SMS — Android will provide a notification if an application attempts to send SMS to a short code that uses premium services which might cause additional charges. The user can choose whether to allow the application to send the message or block it.
• Always-on VPN — VPN can be configured so that applications will not have access to the network until a VPN connection is established. This prevents applications from sending data across other networks.
• Certificate Pinning — The libcore SSL implementation now supports certificate pinning. Pinned domains will receive a certificate validation failure if the certificate does not chain to a set of expected certificates. This protects against possible compromise of Certificate Authorities.
• Improved display of Android permissions — Permissions have been organized into groups that are more easily understood by users. During review of the permissions, the user can click on the permission to see more detailed information about the permission.
• installd hardening — The installd daemon does not run as the root user, reducing potential attack surface for root privilege escalation.
• init script hardening — init scripts now apply O_NOFOLLOW semantics to prevent symlink related attacks.
• FORTIFY_SOURCE — Android now implements FORTIFY_SOURCE. This is used by system libraries and applications to prevent memory corruption.
• ContentProvider default configuration — Applications which target API level 17 will have “export” set to “false” by default for each ContentProvider, reducing default attack surface for applications.
• Cryptography — Modified the default implementations of SecureRandom and Cipher.RSA to use OpenSSL. Added SSLSocket support for TLSv1.1 and TLSv1.2 using OpenSSL 1.0.1
• Security Fixes — Upgraded open source libraries with security fixes include WebKit, libpng, OpenSSL, and LibXML. Android 4.2 also includes fixes for Android-specific vulnerabilities. Information about these vulnerabilities has been provided to Open Handset Alliance members and fixes are available in Android Open Source Project. To improve security, some devices with earlier versions of Android may also include these fixes.

New Bluetooth stack

Android 4.2 introduces a new Bluetooth stack optimized for use with Android devices. The new Bluetooth stack developed in collaboration between Google and Broadcom replaces the stack based on BlueZ and provides improved compatibility and reliability.

Low-latency audio

Android 4.2 improves support for low-latency audio playback, starting from the improvements made in Android 4.1 release for audio output latency using OpenSL ES, Soundpool and tone generator APIs. These improvements depend on hardware support — devices that offer these low-latency audio features can advertise their support to apps through a hardware feature constant. New AudioManager APIs are provided to query the native audio sample rate and buffer size, for use on devices which claim this feature.

New camera hardware interface

Android 4.2 introduces a new implementation of the camera stack. The camera subsystem includes the implementations for components in the camera pipeline such as burst mode capture with processing controls.

New NFC hardware interface and controller interface

Android 4.2 introduces support for controllers based on the NCI standard from the NFC-Forum. NCI provides a standard communication protocol between an NFC Controller (NFCC) and a device Host, and the new NFC stack developed in collaboration between Google and Broadcom supports it.

Dalvik runtime optimizations

The Dalvik runtime includes enhancements for performance and security across a wider range of architectures:

• x86 JIT support from Intel and MIPS JIT support from MIPS
• Optimized garbage-collection parameters for devices with > 512MB
• Default implementations of SecureRandom and Cipher.RSA now use OpenSSL
• SSLSocket support for TLSv1.1 and TLSv1.2 via OpenSSL 1.0.1
• New intrinsic support for StrictMath methods abs, min, max, and sqrt
• BouncyCastle updated to 1.47
• zlib updated to 1.27
• dlmalloc updated to 2.8.6

Welcome to Android 4.1 the first version of Jelly Bean!

Android 4.1 is the fastest and smoothest version of Android yet. We’ve made improvements throughout the platform and added great new features for users and developers. This document provides a glimpse of what's new for developers.

See the Android 4.1 APIs document for a detailed look at the new developer APIs.

Find out more about the Jelly Bean features for users at www.android.com.

Faster, Smoother, More Responsive

Android 4.1 is optimized to deliver Android's best performance and lowest touch latency, in an effortless, intuitive UI.

To ensure a consistent framerate, Android 4.1 extends vsync timing across all drawing and animation done by the Android framework. Everything runs in lockstep against a 16 millisecond vsync heartbeat — application rendering, touch events, screen composition, and display refresh — so frames don’t get ahead or behind.

Android 4.1 also adds triple buffering in the graphics pipeline, for more consistent rendering that makes everything feel smoother, from scrolling to paging and animations.

Android 4.1 reduces touch latency not only by synchronizing touch to vsync timing, but also by actually anticipating where your finger will be at the time of the screen refresh. This results in a more reactive and uniform touch response. In addition, after periods of inactivity, Android applies a CPU input boost at the next touch event, to make sure there’s no latency.

Tooling can help you get the absolute best performance out of your apps. Android 4.1 is designed to work with a new tool called systrace, which collects data directly from the Linux kernel to produce an overall picture of system activities. The data is represented as a group of vertically stacked time series graphs, to help isolate rendering interruptions and other issues. The tool is available now in the Android SDK (Tools R20 or higher)

New Ways to Create Beautiful UI

Expandable notifications

Notifications have long been a unique and popular feature on Android. Developers can use them to place important or time-based information in front of users in the notification bar, outside of the app’s normal UI.

Android 4.1 brings a major update to the Android notifications framework. Apps can now display larger, richer notifications to users that can be expanded and collapsed with a pinch or swipe. Notifications support new types of content, including photos, have configurable priority, and can even include multiple actions.

Through an improved notification builder, apps can create notifications that use a larger area, up to 256 dp in height. Three templated notification styles are available:

• BigTextStyle — a notification that includes a multiline TextView object.
• BigInboxStyle — a notification that shows any kind of list such as messages, headlines, and so on.
• BigPictureStyle — a notification that showcases visual content such as a bitmap.

In addition to the templated styles, you can create your own notification styles using any remote View.

Apps can add up to three actions to a notification, which are displayed below the notification content. The actions let the users respond directly to the information in the notification in alternative ways. such as by email or by phone call, without visiting the app.

With expandable notifications, apps can give more information to the user, effortlessly and on demand. Users remain in control and can long-press any notification to get information about the sender and optionally disable further notifications from the app.

Simplified task navigation

Android 4.1 makes it easy for you to manage the “Up” navigation that’s available to users from inside of your apps and helps ensure a consistent experience for users.

You can define the intended Up navigation for individual Activity components of your UI by adding a new XML attribute in the app’s manifest file. At run time, as Activities are launched, the system extracts the Up navigation tree from the manifest file and automatically creates the Up affordance navigation in the action bar. Developers who declare Up navigation in the manifest no longer need to manage navigation by callback at run time, although they can also do so if needed.

Also available is a new TaskStackBuilder class that lets you quickly put together a synthetic task stack to start immediately or to use when an Activity is launched from a PendingIntent. Creating a synthetic task stack is especially useful when users launch Activities from remote views, such as from Home screen widgets and notifications, because it lets the developer provide a managed, consistent experience on Back navigation.

Easy animations for Activity launch

You can use a new helper class, ActivityOptions, to create and control the animation displayed when you launch your Activities. Through the helper class, you can specify custom animation resources to be used when the activity is launched, or request new zoom animations that start from any rectangle you specify on screen and that optionally include a thumbnail bitmap.

Transitions to Lights Out and Full Screen Modes

New system UI flags in View let you to cleanly transition from a normal application UI (with action bar, navigation bar, and system bar visible), to "lights out mode" (with status bar and action bar hidden and navigation bar dimmed) or "full screen mode" (with status bar, action bar, and navigation bar all hidden).

New types of remoteable Views

Developers can now use GridLayout and ViewStub views in Home screen widgets and notifications. GridLayout lets you structure the content of your remote views and manage child views alignments with a shallower UI hierarchy. ViewStub is an invisible, zero-sized View that can be used to lazily inflate layout resources at runtime.

Live wallpaper preview

Android 4.1 makes it easier for users to find and install Live Wallpapers from apps that include them. If your app includes Live Wallpapers, you can now start an Activity (ACTION_CHANGE_LIVE_WALLPAPER) that shows the user a preview of the Live Wallpaper from your own app. From the preview, users can directly load the Live Wallpaper.

Higher-resolution contact photos

With Android 4.1, you can store contact photos that are as large as 720 x 720, making contacts even richer and more personal. Apps can store and retrieve contact photos at that size or use any other size needed. The maximum photo size supported on specific devices may vary, so apps should query the built-in contacts provider at run time to obtain the max size for the current device.

New Input Types and Capabilities

Find out about devices being added and removed

Apps can register to be notified when any new input devices are attached, by USB, Bluetooth, or any other connection type. They can use this information to change state or capabilities as needed. For example, a game could receive notification that a new keyboard or joystick is attached, indicating the presence of a new player.

Query the capabilities of input devices

Android 4.1 includes APIs that let apps and games take full advantage of all input devices that are connected and available.

Apps can query the device manager to enumerate all of the input devices currently attached and learn about the capabilities of each.

Control vibrator on input devices

Among other capabilities, apps can now make use of any vibrator service associated with an attached input device, such as for Rumble Pak controllers.

Animation and Graphics

Vsync for apps

Extending vsync across the Android framework leads to a more consistent framerate and a smooth, steady UI. So that apps also benefit, Android 4.1 extends vsync timing to all drawing and animations initiated by apps. This lets them optimize operations on the UI thread and provides a stable timebase for synchronization.

Apps can take advantage of vsync timing for free, through Android’s animation framework. The animation framework now uses vsync timing to automatically handle synchronization across animators.

For specialized uses, apps can access vsync timing through APIs exposed by a new Choreographer class. Apps can request invalidation on the next vsync frame — a good way to schedule animation when the app is not using the animation framework. For more advanced uses, apps can post a callback that the Choreographer class will run on the next frame.

New animation actions and transition types

The animation framework now lets you define start and end actions to take when running ViewPropertyAnimator animations, to help synchronize them with other animations or actions in the application. The action can run any runnable object. For example, the runnable might specify another animation to start when the previous one finishes.

You can also now specify that a ViewPropertyAnimator use a layer during the course of its animation. Previously, it was a best practice to animate complicated views by setting up a layer prior to starting an animation and then handling an onAnimationEnd() event to remove the layer when the animation finishes. Now, the withLayer() method on ViewPropertyAnimator simplifies this process with a single method call.

A new transition type in LayoutTransition enables you to automate animations in response to all layout changes in a ViewGroup.

New Types of Connectivity

Android Beam

Android Beam is a popular NFC-based technology that lets users instantly share, just by touching two NFC-enabled phones together.

In Android 4.1, Android Beam makes it easier to share images, videos, or other payloads by leveraging Bluetooth for the data transfer. When the user triggers a transfer, Android Beam hands over from NFC to Bluetooth, making it really easy to manage the transfer of a file from one device to another.

Wi-Fi Network Service Discovery

Android 4.1 introduces support for multicast DNS-based service discovery, which lets applications find and connect to services offered by peer devices over Wi-Fi networks — including mobile devices, printers, cameras, media players, and others. Developers can take advantage of Wi-Fi network service discovery to build cross-platform or multiplayer games and application experiences.

Using the service discovery API, apps can create and register any kind of service, for any other NSD-enabled device to discover. The service is advertised by multicast across the network using a human-readable string identifier, which lets user more easily identify the type of service.

Consumer devices can use the API to scan and discover services available from devices connected to the local Wi-Fi network. After discovery, apps can use the API to resolve the service to an IP address and port through which it can establish a socket connection.

You can take advantage of this API to build new features into your apps. For example, you could let users connect to a webcam, a printer, or an app on another mobile device that supports Wi-Fi peer-to-peer connections.

Wi-Fi Direct Service Discovery

Ice Cream Sandwich introduced support for Wi-Fi Direct, a technology that lets apps discover and pair directly, over a high-bandwidth peer-to-peer connection. Wi-Fi Direct is an ideal way to share media, photos, files and other types of data and sessions, even where there is no cell network or Wi-Fi available.

Android 4.1 takes Wi-Fi Direct further, adding API support for pre-associated service discovery. Pre-associated service discovery lets your apps get more useful information from nearby devices about the services they support, before they attempt to connect. Apps can initiate discovery for a specific service and filter the list of discovered devices to those that actually support the target service or application.

For example, this means that your app could discover only devices that are “printers” or that have a specific game available, instead of discovering all nearby Wi-Fi Direct devices. On the other hand, your app can advertise the service it provides to other devices, which can discover it and then negotiate a connection. This greatly simplifies discovery and pairing for users and lets apps take advantage of Wi-Fi Direct more effectively.

With Wi-Fi Direct service discovery, you can create apps and multiplayer games that can share photos, videos, gameplay, scores, or almost anything else — all without requiring any Internet or mobile network. Your users can connect using only a direct p2p connection, which avoids using mobile bandwidth.

Network Bandwidth Management

Android 4.1 helps apps manage data usage appropriately when the device is connected to a metered network, including tethering to a mobile hotspot. Apps can query whether the current network is metered before beginning a large download that might otherwise be relatively expensive to the user. Through the API, you can now get a clear picture of which networks are sensitive to data usage and manage your network activity accordingly.

New Media Capabilities

Media codec access

Android 4.1 provides low-level access to platform hardware and software codecs. Apps can query the system to discover what low-level media codecs are available on the device and then and use them in the ways they need. For example, you can now create multiple instances of a media codec, queue input buffers, and receive output buffers in return. In addition, the media codec framework supports protected content. Apps can query for an available codec that is able to play protected content with a DRM solution available on the the device.

USB Audio

USB audio output support allows hardware vendors to build hardware such as audio docks that interface with Android devices. This functionality is also exposed with the Android Open Accessory Development Kit (ADK) to give all developers the chance to create their own hardware.

Audio record triggering

Android now lets you trigger audio recording based on the completion of an audio playback track. This is useful for situations such as playing back a tone to cue your users to begin speaking to record their voices. This feature helps you sync up recording so you don’t record audio that is currently being played back and prevents recordings from beginning too late.

Multichannel audio

Android 4.1 supports multichannel audio on devices that have hardware multichannel audio out through the HDMI port. Multichannel audio lets you deliver rich media experiences to users for applications such as games, music apps, and video players. For devices that do not have the supported hardware, Android automatically downmixes the audio to the number of channels that are supported by the device (usually stereo).

Android 4.1 also adds built-in support for encoding/decoding AAC 5.1 audio.

Audio preprocessing

Developers can apply preprocessing effects to audio being recorded, such as to apply noise suppression for improving speech recording quality, echo cancellation for acoustic echo, and auto gain control for audio with inconsistent volume levels. Apps that require high quality and clean audio recording will benefit from these preprocessors.

Audio chaining

MediaPlayer supports chaining audio streams together to play audio files without pauses. This is useful for apps that require seamless transitions between audio files such as music players to play albums with continuous tracks or games.

Media Router

The new APIs MediaRouter, MediaRouteActionProvider, and MediaRouteButton provide standard mechanisms and UI for choosing where to play media. Support is built-in for wired headsets and a2dp bluetooth headsets and speakers, and you can add your own routing options within your own app.

Renderscript Computation

Android 4.1 extends Renderscript computation to give you more flexibility. You can now sample textures in your Renderscript compute scripts, and new pragmas are available to define the floating point precision required by your scripts. This lets you enable NEON instructions such as fast vector math operations on the CPU path, that wouldn’t otherwise be possible with the full IEEE 754-2008 standard.

You can now debug your Renderscript compute scripts on x86-based emulator and hardware devices. You can also define multiple root-style kernels in a single Renderscript source file.

Android Browser and WebView

In Android 4.1, the Android Browser and WebViews include these enhancements:

• Better HTML5 video user experience, including touch-to-play/pause and smooth transition from inline to full screen mode.
• Improved rendering speed and reduced memory usage for better scrolling and zooming performance.
• Improved HTML5/CSS3/Canvas animation performance.
• Improved text input.
• Updated JavaScript Engine (V8) for better JavaScript performance.
• Support for the updated HTML5 Media Capture specification (the "capture" attribute on input type=file elements).

Google APIs and services

To extend the capabilities of Android even further, several new services for Android are available.

Google Cloud Messaging for Android

Google Cloud Messaging (GCM) is a service that lets developers send short message data to their users on Android devices, without needing a proprietary sync solution.

GCM handles all the details of queuing messages and delivering them efficiently to the targeted Android devices. It supports message multicasting and can reach up to 1000 connected devices simultaneously with a single request. It also supports message payloads, which means that in addition to sending tickle messages to an app on the device, developers can send up to 4K of data.

Google Cloud Messaging is completely free for all developers and sign-up is easy. See the Google Cloud Messaging page for registration, downloads, and documentation.

App Encryption

Starting with Android 4.1, Google Play will help protect application assets by encrypting all paid apps with a device-specific key before they are delivered and stored on a device.

Smart App Updates

Smart app updates is a new feature of Google Play that introduces a better way of delivering app updates to devices. When developers publish an update, Google Play now delivers only the bits that have changed to devices, rather than the entire APK. This makes the updates much lighter-weight in most cases, so they are faster to download, save the device’s battery, and conserve bandwidth usage on users’ mobile data plan. On average, a smart app update is about 1/3 the size of a full APK update.

Google Play services

Google Play services helps developers to integrate Google services such as authentication and Google+ into their apps delivered through Google Play.

Google Play services is automatically provisioned to end user devices by Google Play, so all you need is a thin client library in your apps.

Because your app only contains the small client library, you can take advantage of these services without a big increase in download size and storage footprint. Also, Google Play will deliver regular updates to the services, without developers needing to publish app updates to take advantage of them.

For more information about the APIs included in Google Play Services, see the Google Play services developer page.