AVPlayer（二）AVAsset

https://www.sunyazhou.com/2017/06/16/Learning-AV-Foundation-AVAsset-Basic/?utm_source=tuicool&utm_medium=referral

AVAsset 专辑

一个抽象类，里面包含曲目、格式、时长, 以及元数据NSData(二进制的bytes).

@property (nonatomic, readonly) NSArray<AVAssetTrack *> *tracks;

加载格式

AVURLAsset *anAsset = [[AVURLAsset alloc] initWithURL:url options:nil];
NSArray *keys = @[@"duration",@"tracks"];

[asset loadValuesAsynchronouslyForKeys:keys completionHandler:^() {
    NSError *error = nil;
    AVKeyValueStatus tracksStatus = [asset statusOfValueForKey:@"tracks" error:&error];
    //根据相应的属性状态进行对应的处理
    switch (tracksStatus) {
        case AVKeyValueStatusUnknown:
                //TODO
            break;
        case AVKeyValueStatusLoading:
                //TODO
            break;
        case AVKeyValueStatusLoaded:
                //TODO
            break;
        case AVKeyValueStatusFailed:
                //TODO
            break;
        case AVKeyValueStatusCancelled:
                //TODO
            break;
   }
}];

AVAssetTrack 曲目

我们真正存储媒体资源的统一媒体类型。

• 音频流
• 视频流

NSArray<AVAssetTrack *> *audioAssetTracks = [asset tracksWithMediaType:AVMediaTypeAudio];
NSArray<AVAssetTrack *> *videoAssetTracks = [asset tracksWithMediaType:AVMediaTypeVideo];

AVAssetImageGenerator

- (instancetype)initWithAsset:(AVAsset *)asset NS_DESIGNATED_INITIALIZER;

//获取一张图片，requestedTime 指定要获取视频中哪个时刻的图片，actualTime 返回图片实际是视频的哪个时刻，outError 返回错误信息
- (nullable CGImageRef)copyCGImageAtTime:(CMTime)requestedTime actualTime:(nullable CMTime *)actualTime error:(NSError * _Nullable * _Nullable)outError CF_RETURNS_RETAINED;

//获取多张图片，每一次图片生成后，都会调用一次 handler
- (void)generateCGImagesAsynchronouslyForTimes:(NSArray<NSValue *> *)requestedTimes completionHandler:(AVAssetImageGeneratorCompletionHandler)handler;

//上述 handler 的类型如下，回调中的参数有图片的请求时刻和实际时刻，图片，状态（成功、失败、取消），错误信息
typedef void (^AVAssetImageGeneratorCompletionHandler)(CMTime requestedTime, CGImageRef _Nullable image, CMTime actualTime, AVAssetImageGeneratorResult result, NSError * _Nullable error);