iOS AVPlayer截取视频首帧缩略图，常规mp4与m3u8

获取常规格式视频缩略图（适用于mp4、mov等）

/**
 *  获取视频的缩略图方法
 *  @param videoUrl 视频链接  支持本地路径和网络路径
 *  @return 视频截图
 */
+ (UIImage *)getVideoImageFromPath:(NSURL *)videoUrl{
    UIImage *shotImage;
    AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoUrl options:nil];
    AVAssetImageGenerator *gen = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    gen.appliesPreferredTrackTransform = YES;
    CMTime time = CMTimeMakeWithSeconds(0.0, 600);
    NSError *error = nil;
    CMTime actualTime;
    CGImageRef image = [gen copyCGImageAtTime:time actualTime:&actualTime error:&error];
    shotImage = [[UIImage alloc] initWithCGImage:image];
    CGImageRelease(image);
    return shotImage;
}

获取m3u8格式视频缩略图

m3u8格式是适用于直播流的格式，加载时是以切片的模式分段加载，无法从视频流中直接获取某一帧图片
这里是使用AVPlayerItemVideoOutput，采用截屏输出的方案来获取首帧图
该方法一定要视频在可播放的状态下才能取到，如果该缩略图时做封面图使用，建议还是和服务端的同事沟通一下参数方案吧

一、声明对象

/// 播放器
@property (nonatomic, strong) AVPlayer *player;
/// 播放器item
@property (nonatomic, strong) AVPlayerItem *playerItem;
/// 播放器layer
@property (nonatomic, strong) AVPlayerLayer *playerLayer;
/// 视频截图输出
@property (nonatomic, strong) AVPlayerItemVideoOutput *output;

二、初始化播放器时，给播放器添加输出对象

//包装到Asset，防止抓包泄露视频地址
AVURLAsset *asset = [AVURLAsset assetWithURL:[NSURL URLWithString:@"视频链接"]];
//创建播放源
self.playerItem = [AVPlayerItem playerItemWithAsset:asset];
//创建播放器
self.player = [AVPlayer playerWithPlayerItem:self.playerItem];
//设置播放控件
self.playerLayer = [AVPlayerLayer playerLayerWithPlayer:self.player];

//已经创建过了，代表已经添加到playerItem中，这里先移除，防止重复
if (self.output) {
    [self.playerItem removeOutput:self.output];
}
NSDictionary *settings = @{(id)kCVPixelBufferPixelFormatTypeKey:@(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)};
self.output = [[AVPlayerItemVideoOutput alloc] initWithPixelBufferAttributes:settings];
[self.playerItem  addOutput:self.output];

播放器销毁时要移除output对象并置为nil

[self.playerItem removeOutput:self.output];
self.output = nil;

三、监听播放器缓存到可以播放的状态

获取首帧缩略图时一定要监听该状态，否则在此之前去截取会失败

//监听缓存足够播放的状态
[self.playerItem addObserver:self forKeyPath:@"playbackLikelyToKeepUp" options:NSKeyValueObservingOptionNew context:nil];

播放器销毁时移除

[self.player.currentItem removeObserver:self forKeyPath:@"playbackLikelyToKeepUp"];

四、去取首帧缩略图

一定要先暂停，不然取到的图片不一定是首帧图，存在着播放中的误差

//播放器状态监听
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"playbackLikelyToKeepUp"]) {//缓冲到足够播放的状态
        [self.player pause];
        //这里等待0.5秒时为了等player绘制完成，否则取不到video缩略图
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            //取缩略图
            UIImage *thumImg = [self getThumbnailImageCompletion];
            [self.player play];
        });
    }
}

核心代码，如果播放器有截屏的功能也可以用该方法，获取当前播放帧的图片

- (UIImage *)getThumbnailImageCompletion{
    UIImage *frameImg = nil;
    //确保当前时间的视频已经加载完成
    CVPixelBufferRef pixelBuffer = [self.output copyPixelBufferForItemTime:self.player.currentTime itemTimeForDisplay:nil];
    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:pixelBuffer];
    CIContext *temporaryContext = [CIContext contextWithOptions:nil];
    CGImageRef videoImage = [temporaryContext createCGImage:ciImage
                                                   fromRect:CGRectMake(0, 0,
                                                 CVPixelBufferGetWidth(pixelBuffer),
                                                 CVPixelBufferGetHeight(pixelBuffer))];
    frameImg = [UIImage imageWithCGImage:videoImage];
    CGImageRelease(videoImage);
    CVBufferRelease(pixelBuffer);
    return frameImg;
}