This component is used to interface with Mac OS's MPNowPlayingInfoCenter and related MediaPlayer API: https://developer.apple.com/documentation/mediaplayer/mpnowplayinginfocenter
This includes an interface for MPRemoteCommandCenter, which can be used to receive media-related user input (e.g. media keys and actions that are available through the MPNowPlayingInfoCenter such as repeat and rating). https://developer.apple.com/documentation/mediaplayer/mpremotecommandcenter
Note that these APIs are only available on Mac OS 10.12.2 or later.
This README.md primarily aims to overview the mac specific components of System Media Controls.
For overview documentation see //content/browser/media/system_media_controls/README.md
Starting in M130, desktop PWAs (dPWAs) have their own instanced System Media Controls. In this folder, the mac specific implementation is implemented to support PWA app shims communicating with MPNowPlayingInfoCenter and related MediaPlayer APIs via SystemMediaControlsBridge.
dPWAs on macOS are hosted using an app shim process, an external process to Chrome that communicates via mojo. This process helps with the dPWA's identity on macOS - as to appear as a standalone application to macOS.
We leverage this app shim process to speak with macOS' media APIs so that dPWAs show up as a separate app to Chromium playing media.
system_media_controls_bridge.h describes a class that can be instantiated sometimes ‘in-process’ (with respect to the browser process) or ‘out-of-process’ (within each dPWA app shim process). This allows us to write the code that speaks to macOS once, but use it from within the browser process for the browser singleton System Media Controls and reuse it any number of times from each app shim process to represent an independent app playing audio.
To achieve this ‘bridge’ concept, remote_cocoa/system_media_controls.mojom describes a communication interface that allows SystemMediaControlsMac to speak with the SystemMediaControlsBridge without knowing whether its core functionality (implemented by ...Bridge) resides in or out of process.
In the scenario that an out of process bridge is required for dPWAs, we leverage the existing ApplicationBridge interface with app shims to facilitate its creation. See //components/remote_cocoa/app_shim/application_bridge.h.
now_playing_info_center_delegate[_cocoa] is used to pass information to macOS.
remote_command_center_deleate[_cocoa] is used to receive messages from macOS such as a request to pause or play.
Design docs are available in the overview documentation here: //content/browser/media/system_media_controls/README.md
