Use the MediaRemote private framework to get and set the playing state of the Touch Bar based on media change events

MediaRemoteEvents.m

// clang -x objective-c -framework Foundation -framework MediaRemote -F /System/Library/PrivateFrameworks TouchBarMediaKeys.m -o TouchBarMediaKeys
// ./TouchBarMediaKeys

#import <Foundation/Foundation.h>
#import <MediaPlayer/MediaPlayer.h>

enum {
    kMRPlaybackStateUnknown = 0,
    kMRPlaybackStatePlaying,
    kMRPlaybackStatePaused,
    kMRPlaybackStateStopped,
    kMRPlaybackStateInterrupted
};
typedef uint32_t MRPlaybackState;

typedef void (^MRMediaRemoteGetNowPlayingApplicationIsPlayingBlock)(BOOL);
typedef struct _MROrigin *MROriginRef;
typedef uint32_t MRMediaRemoteError;
typedef void (^MRMediaRemoteGetNowPlayingApplicationPlaybackStateCompletion)(MRPlaybackState playbackState);

void MRMediaRemoteSetNowPlayingApplicationOverrideEnabled(BOOL);
void MRMediaRemoteRegisterForNowPlayingNotifications(dispatch_queue_t);
BOOL MRMediaRemoteSetCanBeNowPlayingApplication(BOOL);
MROriginRef MRMediaRemoteGetLocalOrigin(void);
void MRMediaRemoteGetNowPlayingApplicationPlaybackState(dispatch_queue_t, MRMediaRemoteGetNowPlayingApplicationPlaybackStateCompletion);
void MRMediaRemoteSetNowPlayingApplicationPlaybackStateForOrigin(MROriginRef, MRPlaybackState, dispatch_queue_t, void(^completion)(MRMediaRemoteError));

extern NSString *kMRMediaRemoteNowPlayingApplicationIsPlayingDidChangeNotification;

@interface TouchBarMediaKeys : NSObject
- (void)nowPlayingChange:(NSNotification *)notification;
@end

@implementation TouchBarMediaKeys
- (void)nowPlayingChange:(NSNotification *)notification {
    MRMediaRemoteGetNowPlayingApplicationPlaybackState(dispatch_get_main_queue(), ^(MRPlaybackState playbackState) {
        NSLog(@"kMRPlaybackStateUnknown: %d", playbackState == kMRPlaybackStateUnknown);
        NSLog(@"kMRPlaybackStatePlaying: %d", playbackState == kMRPlaybackStatePlaying);
        NSLog(@"kMRPlaybackStateStopped: %d", playbackState == kMRPlaybackStateStopped);
        NSLog(@"kMRPlaybackStatePaused: %d", playbackState == kMRPlaybackStatePaused);
        NSLog(@"kMRPlaybackStateInterrupted: %d", playbackState == kMRPlaybackStateInterrupted);
    });

    // Set playback state to playing
    // MRMediaRemoteSetNowPlayingApplicationPlaybackStateForOrigin(MRMediaRemoteGetLocalOrigin(), kMRPlaybackStatePlaying, dispatch_get_main_queue(), ^(MRMediaRemoteError error) {});
    // Set playback state to stopped
    // MRMediaRemoteSetNowPlayingApplicationPlaybackStateForOrigin(MRMediaRemoteGetLocalOrigin(), kMRPlaybackStateStopped, dispatch_get_main_queue(), ^(MRMediaRemoteError error) {});
  }
@end

int main(int argc, const char *argv[]) {
  @autoreleasepool {
    TouchBarMediaKeys *touchBarMediaKeys = [[TouchBarMediaKeys alloc] init];
    [[NSNotificationCenter defaultCenter]
        addObserver:touchBarMediaKeys
        selector:@selector(nowPlayingChange:)
        name:kMRMediaRemoteNowPlayingApplicationIsPlayingDidChangeNotification
        object:nil];
    MRMediaRemoteRegisterForNowPlayingNotifications(dispatch_get_main_queue());
    MRMediaRemoteSetCanBeNowPlayingApplication(YES);

    [[NSRunLoop currentRunLoop] run];
  }
  return 0;
}

This rocks! thank you