iOS 解决AVPlayerLayer（有声音）无法显示

背景：有一个详情页面，页面的上半部分需要播放一段mp4视频。
流程：进入页面先将播放器渲染好，请求网络得到mp4地址自动播放。
网上查找相关资料需要用AVFoundation库的中的三个类：
1、AVPlayerItem
2、AVPlayer
3、AVPlayerLayer

DetailHeaderView.h代码

#import "BaseView.h"

#import <AVFoundation/AVFoundation.h>

NS_ASSUME_NONNULL_BEGIN

@class MealModel;
@interface DetailHeaderView : BaseView

@property (nonatomic,strong) AVPlayer *player;
@property (nonatomic,strong) AVPlayerLayer *playerLayer;
@property (nonatomic,strong) UIImageView *background;

- (void)loadData:(MealModel *)data;

@end

NS_ASSUME_NONNULL_END

DetailHeaderView.m代码

#import "DetailHeaderView.h"
#import "MealModel.h"

@implementation DetailHeaderView

- (UIImageView *)background {
    if (!_background) {
        _background = [[UIImageView alloc] initWithFrame:self.bounds];
        _background.image = [UIImage imageNamed:@"视频默认图-1"];
    }
    return _background;
}

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

- (AVPlayerLayer *)playerLayer {
    if (!_playerLayer) {
       _playerLayer = [[AVPlayerLayer alloc] initWithLayer:self.player];
        _playerLayer.frame = self.bounds;
        _playerLayer.backgroundColor = [UIColor blackColor].CGColor;
        _playerLayer.videoGravity = AVLayerVideoGravityResizeAspect;
    }
    return _playerLayer;
}

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        self.backgroundColor = [UIColor random];
        [self.layer addSublayer:self.playerLayer];
    }
    return self;
}

- (void)loadData:(MealModel *)data {
    if (data.videoDesc.length > 0) {
        NSURL *url = [NSURL URLWithString:data.videoDesc];
        AVPlayerItem *item = [AVPlayerItem playerItemWithURL:url];
        [self.player replaceCurrentItemWithPlayerItem:item];
        [self.player play];
    } else {
        [self addSubview:self.background];
    }
}

@end

运行的结果：是（iOS）AVPlayer有声音没有画面！！！
需将
_playerLayer = [[AVPlayerLayer alloc] initWithLayer:self.player];
改为
_playerLayer = [[AVPlayerLayer alloc] init];
再将
[self.player replaceCurrentItemWithPlayerItem:item];
后面添加
[self.playerLayer setPlayer:self.player];