Android 3.1 is an incremental release that builds on the tablet-optimized UI and features introduced in Android 3.0. It adds several new features for users and developers, including:
- Open Accessory API. This new API provides a way for Android applications to integrate and interact with a wide range of accessories such as musical equipment, exercise equipment, robotics systems, and many others.
- USB host API. On devices that support USB host mode, applications can now manage connected USB peripherals such as audio devices. input devices, communications devices, and more.
- Input from mice, joysticks, and gamepads. Android 3.1 extends the input event system to support a variety of new input sources and motion events such as from mice, trackballs, joysticks, gamepads, and others.
- Resizable Home screen widgets. Developers can now create Home screen widgets that are resizeable horizontally, vertically, or both.
- Media Transfer Protocol (MTP) Applications can now receive notifications when external cameras are attached and removed, manage files and storage on those devices, and transfer files and metadata to and from them.
- Real-time Transport Protocol (RTP) API for audio. Developers can directly manage on-demand or interactive data streaming to enable VOIP, push-to-talk, conferencing, and audio streaming.