* Blue: Internal listeners; all except `MediaDataManager` and `ResumeMediaBrowser` implement [`MediaDataManager.Listener`](/packages/SystemUI/src/com/android/systemui/media/MediaDataManager.kt#711) and receive `onMediaDataLoaded` and `onMediaDataRemoved` events
## Classes
Files under [`systemui/media/`](/packages/SystemUI/src/com/android/systemui/media/):
* UI
*`dialog/`
* Output switcher dialog (maintained by Settings team)
* IlluminationDrawable.kt
* LightSourceDrawable.kt
* These create the glow animation when you tap on a button (see [`qs_media_light_source`](/packages/SystemUI/res/drawable/qs_media_light_source.xml)). Should be reusable in other layouts.
* Carousel:
* MediaCarouselController.kt
* Keeps the carousel view up to date and handles state changes (e.g. expansion)
* Handles settings gear and page indicator
* MediaCarouselScrollHandler.kt
* Handles scrolling between players in the carousel
* MediaScrollView.kt
* Scrollview used in the carousel layout, has some custom measurement code
* Individual players:
* KeyguardMediaController.kt
* Lockscreen media controls have a special wrapper in order to work with the existing lockscreen notification layout
* MediaControlPanel.java
* Main class for media control UI
* SeekBarObserver.kt
* Updates seekbar state
* SeekBarViewModel.kt
* Implements its own `computePosition()` for the seekbar (to avoid continually polling the `PlaybackState`, which involves binder calls)
* Does some touch falsing (ignore flings, require drags to start near the thumb - otherwise users would often accidentally trigger the seekbar when they meant to move the carousel or shade)
* PlayerViewHolder.kt
* Holds references to the UI elements in the panel
* Animation support:
* MediaHierarchyManager.kt
* Responsible for placement of media view and animation between hosts
* MediaHost.kt
* Every location that a media player could be located needs a `MediaHost`
* Tracks configuration (if it should show inactive media, needs falsing, etc.)
* MediaHostStatesManager.kt
* Manages the various media host states and coordinates heights between different players
* Has the most up to date state for any location
* MediaViewController.kt
* Controls a single instance of a media player, keeps the media view states up to date
* Backend
* MediaData.kt
* Holds all the media data (track info, active/resume state, etc.)
* MediaDataCombineLatest.kt
* Combines update events from `MediaDataManager` and `MediaDeviceManager`, so that downstream listeners will have device info
* MediaDataFilter.kt
* Filters media data based on the current user
* Exit point for the pipeline: "external listeners" (currently `MediaHost` and `MediaCarouselController`), while they should be added via `MediaDataManager.addListener()`, will actually be listening to this output
* MediaDataManager.kt
* Entry point for the pipeline; initializes listener connections and assigns external listeners to the correct exit point
* Converts media notifications and resumable media info into `MediaData`
* MediaDeviceManager.kt
* Handles device updates
* MediaFeatureFlag.kt
* Utility to check whether media controls are enabled
* MediaSessionBasedFilter.kt
* Filters media events based on media session. This prevents duplicate controls in situations like casting where we might get both a local and remote object for the same media session.
* MediaTimeoutListener.kt
* Listens to `PlaybackState` and marks controls inactive after the media has been paused/stopped for 10 minutes (value can be adjusted locally with `adb shell setprop debug.sysui.media_timeout [ms]`)
* MediaResumeListener.kt
* Listens for new media data and attempts to find a valid `MediaBrowserService` for the app. If successful, sends the information back to the `MediaDataManager`
* Saves up to 5 valid `MediaBrowserService` components found this way, and queries them for recent media on boot or user change
* Note: the user can disable this feature completely (or block certain apps from being resumable) in [Settings](https://source.corp.google.com/android/packages/apps/Settings/src/com/android/settings/sound/ResumableMediaAppsController.java), in which case this listener will do nothing (or ignore updates from the blocked apps).
* ResumeMediaBrowser.java
* Connects to an app's [`MediaBrowser`](https://developer.android.com/reference/android/media/browse/MediaBrowser) to determine whether SystemUI is able to connect and find a recent [`MediaItem`](https://developer.android.com/reference/android/media/browse/MediaBrowser.MediaItem)
* Factory classes (for unit testing):
* LocalMediaManagerFactory.kt
* MediaBrowserFactory.java
* MediaControllerFactory.java
* ResumeMediaBrowserFactory.java
## Miscellaneous
Other useful documents:
*[go/sysui-media-resumption-requirements](https://goto.google.com/sysui-media-resumption-requirements) - Internal documentation for app developers about how to work with media resumption
*[Playing nicely with media controls](https://android-developers.googleblog.com/2020/08/playing-nicely-with-media-controls.html) - blog post on the Android 11 updates
