AirPlay is a proprietary protocol stack/suite developed by Apple Inc. that allows wireless streaming between devices of audio, video, device screens, and photos, together with related metadata. Originally implemented only in Apple's software and devices, it was called AirTunes and used for audio only. Apple has since licensed the AirPlay protocol stack as a third-party software component technology to manufacturer partners for them to use in their products in order to be compatible with Apple's devices.
At Apple's annual WWDC conference held on the 5th June 2017, Apple announced AirPlay 2, whose release will coincide with the release of iOS 11 in the third quarter of 2017. AirPlay 2 will offer "multi-room audio" from iOS devices, enabling users to easily control speakers using Control Center, the Home app or Siri. Previously this was only available using iTunes under MacOS or Windows.
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Implementations
There are two types of AirPlay devices, those that send audiovisual content, and those capable of receiving the content and rendering it on displays and speakers.
Senders
AirPlay sender devices include computers running iTunes, and iOS devices such as iPhones, iPods, and iPads running iOS 4.2 or greater. OS X Mountain Lion supports display mirroring via AirPlay on systems containing 2nd generation Intel Core processors or later. There are third party streamers such as AirFoil.
In 2016 HTC released an Android phone with Apple AirPlay streaming.
As of iOS 4.3, third-party apps may send compatible audio and video streams over AirPlay. The iTunes Remote app on iOS can be used to control media playback and select AirPlay streaming receivers for iTunes running on a Mac or PC.
Receivers
AirPlay receiver devices include AirPort Express (which includes a combined analog and optical S/PDIF audio output connector), Apple TV, HomePod and other third party speakers. With the open source implementations of the AirPlay protocol any computer can now be turned into an AirPlay receiver.
However, because not all third-party receivers implement Apple's DRM encryption, some media, such as iTunes Store's own rights-protected music (Apple's own "FairPlay" encryption), YouTube and Netflix, cannot stream to those devices or software. On Apple TV starting with firmware 6.0, the "FairPlay" encryption scheme is enforced and sending devices not supporting it cannot be used.
AirPlay wireless technology is integrated into speaker docks, AV receivers, and stereo systems from companies such as Bose, Yamaha, Philips, Marantz, Bowers & Wilkins, Pioneer, Sony, McIntosh, and Denon. Song titles, artists, album names, elapsed and remaining time, and album artwork can appear on AirPlay-enabled speakers with graphical displays. Often these receivers are built to only support the audio component of AirPlay, much like AirTunes.
Bluetooth devices (headsets, speakers) that support the A2DP profile also appear as AirPlay receivers when paired with an iOS device, although Bluetooth is a device-to-device protocol that does not rely on a wireless network access point.
There are third party receivers such as AirServer, 5KPlayer , Reflector 2, Kodi and TuneAero (audio).
Protocols
AirPlay and AirTunes work over Wi-Fi. Originally, devices had to be connected to the same Wi-Fi network, but since iOS 8 devices can use some kind of ad-hoc mode and thus do not require an existing Wi-Fi network.
The AirTunes part of the AirPlay protocol stack uses UDP for streaming audio and is based on the RTSP network control protocol. The streams are transcoded using the Apple Lossless codec with 44100 Hz and 2 channels symmetrically encrypted with AES, requiring the receiver to have access to the appropriate key to decrypt the streams. The stream is buffered for approximately 2 seconds before playback begins, resulting in a small delay before audio is output after starting an AirPlay stream.
The protocol supports metadata packets that determine the final output volume on the receiving end. This makes it possible to always send audio data unprocessed at its original full volume, preventing sound quality deterioration due to reduction in bit depth and thus sound quality which would otherwise occur if changes in volume were made to the source stream before transmitting. It also makes possible the streaming of one source to multiple targets each with its own volume control.
The AirPort Express' streaming media capabilities use Apple's Remote Audio Output Protocol (RAOP), a proprietary variant of RTSP/RTP. Using WDS-bridging, the AirPort Express can allow AirPlay functionality (as well as Internet access, file and print sharing, etc.) across a larger distance in a mixed environment of wired and up to 10 wireless clients.
AirPlay Mirroring
At WWDC 2011, Jobs announced AirPlay Mirroring as a feature in iOS 5 where the user can stream the screen from an iPad 2 to a HDTV wirelessly and securely without the need for cables.
AirPlay Mirroring is a slightly different technology that allows specific content to be broadcast from a variety of iOS devices and iTunes to a second generation Apple TV. The exact composition of the protocols that AirPlay Mirroring uses have not yet fully been discovered, or reverse-engineered. However, an unofficial AirPlay protocol specification is available. A 2nd generation or later Apple TV is required, and supported hardware (when using OS X Mountain Lion or later) includes the iMac (mid 2011 or newer), Mac mini (mid 2011 or newer), MacBook Air (mid 2011 or newer), MacBook Pro (early 2011 or newer) and the Mac Pro (late 2013 or newer).
Reverse engineering
When the protocol was known as AirTunes, it was reverse-engineered by Jon Lech Johansen in 2004.
On April 8, 2011, James Laird reverse-engineered and released the private key used by the Apple AirPort Express to decrypt incoming audio streams. The release of this key means that third-party software and devices modified to use the key will be able to decrypt and play back or store AirPlay streams. Laird released ShairPort as an example of an audio-only software receiver implementation of AirPlay. Soon more followed and in 2012 the first AirPlay audio and video receiver for PC came with a product called AirServer.
Source of the article : Wikipedia
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