Media Keys - macOS
Currently, macOS offers no reasonable method for sandboxed applications to use the built-in media keys. Downcast supports two methods of working around this problem:
Option 1 - Install BeardedSpice (Recommended)
BeardedSpice is a menu bar application that intelligently manages delivery of media key events to supported applications. It allows Downcast, iTunes, and other AV apps to peacefully coexist and share the media keys.
Option 2 - Hotkeys
Downcast supports setting up global hotkeys as an alternative to using the standard media keys. While you cannot create a hotkey for media keys alone, you can do so for modified media keys. An example would be F9 (by pressing fn, then F9) for playing & pausing. Hotkeys can be created for Play/Pause, Previous, Next, Skip Back, and Skip Forward. The Skip Back and Skip Forward hotkeys are used to skip by the corresponding Skip Forward Interval and Skip Back Interval preferences.
Downcast already has various shortcuts for all of these functions when the app is the focused app (see the Now Playing menu). Hotkeys are in addition to these and are active when Downcast is running.
To setup hotkeys, open Downcast's Preferences window and select the Hotkeys tab.