@interface ViewController ()

@property (strong, nonatomic) AVPlayer *player;
@property (assign, nonatomic) NSInteger index;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
}

- (IBAction)buttonPressed:(UIButton *)sender {
    [self.player.currentItem removeObserver:self forKeyPath:@"status"];
    NSLog(@"removed %@", self.player.currentItem);

    AVPlayerItem *item = [[AVPlayerItem alloc] initWithURL:[NSURL URLWithString:self.urls[self.index]]];

    [item addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:nil];
    NSLog(@"added %@", item);

    [self.player replaceCurrentItemWithPlayerItem:item];

}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"status"]) {
        if ([object isMemberOfClass:[AVPlayerItem class]]) {
            AVPlayerItem *playerItem = (AVPlayerItem *)object;
            switch (playerItem.status) {
                case AVPlayerItemStatusFailed:
                    NSLog(@"failed");
                    break;
                case AVPlayerItemStatusReadyToPlay:
                    NSLog(@"ready");
                    break;
                case AVPlayerItemStatusUnknown:
                    NSLog(@"unknown");
                    break;
            }
        }
    }
}

- (AVPlayer *)player {
    if (!_player) {
        _player = [[AVPlayer alloc] init];
    }
    return _player;
}

- (NSArray *)urls {
    return @[@"https://of92d29bn.qnssl.com/record1.m4a", @"https://of92d29bn.qnssl.com/record2.m4a"];
}

- (NSInteger)index {
    if (_index == 0) {
        _index = 1;
    } else {
        _index = 0;
    }
    return _index;
}