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PlaybackController Interface

The Engine provides a platform interface aace::alexa::PlaybackController for the platform implementation to report on-device transport control button presses for media playing through Alexa. For example, if the user presses the on-screen pause button while listening to Amazon Music through Alexa's AudioPlayer interface, the platform implementation calls a PlaybackController method to report the button press to the Engine.

Note: PlaybackController method calls to manage AudioPlayer's state or playback queue proactively report button presses or the equivalent so that Alexa can react; they do not report changes to the playback state that happen locally first. The Alexa cloud manages the playback queue for AudioPlayer content, so each PlaybackController method call is a request for Alexa to act on the user's local request. The result of the request will come as one or more method invocations on the AudioOutput associated with the channel used for AudioPlayer.

Note: If your implementation needs to stop AudioPlayer media in response to system events, such as audio focus transitions to audio playing outside the scope of the Auto SDK, use PlaybackController to notify the Engine of such changes. However, keep in mind that the expected usage of the interface does not change when it is used in this use case.

Note: PlaybackController only controls media coming from Alexa, i.e. the AudioPlayer. PlaybackController should not be used with the expectation of controlling playback for non-media Alexa audio sources like SpeechSynthesizer or Alexa-aware external media sources integrated with ExternalMediaAdapter or LocalMediaSource. Additionally, calling a PlaybackController method while audio is playing through another Alexa-aware external media source will produce unexpected results and is not recommended.

Whenever Alexa plays media through AudioPlayer, the Engine calls the platform interface method aace::alexa::TemplateRuntime::renderPlayerInfo() to provide visual metadata associated with the media that your implementation should render for the end user. The payload of this method includes descriptions of GUI controls to be displayed and the state in which to display them. When the user interacts with these on-screen controls, your implementation must use the PlaybackController interface to report the button presses to the Engine.

The table below maps the controls from the renderPlayerInfo() payload to the corresponding calls in PlaybackController.

RenderPlayerInfo control name PlaybackController

To implement a custom handler for the playback controller, extend the PlaybackController class:

#include <AACE/Alexa/PlaybackController.h>
class MyPlaybackController : public aace::alexa::PlaybackController {

    void platformPlayButtonPressed() { // called by some platform event

    void platformScrubForwardGUIButtonPressed(){ //called by the platform on an available GUI button event

    void platformShuffleGUIButtonPressed(){ //called by the platform on an available GUI toggle event
        togglePressed(PlaybackToggle::SHUFFLE, true); //the action should send the value opposing the last playerinfo state for that toggle control

// Register the platform interface with the Engine
engine->registerPlatformInterface( std::make_shared<MyPlaybackController>() );
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