let asset = AVAsset(url: videoURL)
let reader = try! AVAssetReader(asset: asset)
let videoTrack = asset.tracks(withMediaType: .video).first!

//输出样本的buffer设置
let outputSettings: [String: Any] = [
    kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)
]
//从视频轨道中读取buffer样本，并输出出来
let readerOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: outputSettings)
reader.add(readerOutput)
reader.startReading()

while reader.status == .reading {
    if let sampleBuffer = readerOutput.copyNextSampleBuffer() {
        // 处理样本数据
    }
}

let writer = try! AVAssetWriter(outputURL: outputURL, fileType: .mp4)
let videoTrack = asset.tracks(withMediaType: .video).first!
//设置写入文件的视频编码
let outputSettings: [String: Any] = [
    AVVideoCodecKey: AVVideoCodecType.h264,
    AVVideoWidthKey: 640,
    AVVideoHeightKey: 480,
]
let writerInput = AVAssetWriterInput(mediaType: .video, outputSettings: outputSettings)
writer.add(writerInput)

let adapter = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: writerInput, sourcePixelBufferAttributes: outputSettings)
writer.startWriting()
writer.startSession(atSourceTime: CMTime.zero)

while // 读取视频数据 {
    if adapter.assetWriterInput.isReadyForMoreMediaData {
        adapter.append(pixelBuffer, withPresentationTime: // 时间戳)
    }
}

writerInput.markAsFinished()
writer.finishWriting {
    // 导出完成
}

/ 本地播放
// let url = Bundle.main.url(forResource: "video", withExtension: "mp4")!
// let playerItem = AVPlayerItem(url: url)
// 网络播放
let url = URL(string: "http://example.com/video.mp4")!
let asset = AVAsset(url: url)
let playerItem = AVPlayerItem(asset: asset)
let player = AVPlayer(playerItem: playerItem)
let playerLayer = AVPlayerLayer(player: player)
playerLayer.frame = view.bounds
view.layer.addSublayer(playerLayer)
player.play()
另外对AVPlayer的其他常见操作还有AVPlayer的pause()、seek(to:)方法，表示暂停、快进；还可以通过KVO监听AVPlayer的状态和播放进度等信息。


AVPlayerViewController提供了常用的播放器控制器界面，包括播放/暂停按钮、播放进度条、播放时间等。可以开箱即用，方便开发。
let playerViewController = AVPlayerViewController()
let url = URL(string: "http://example.com/video.mp4")!
let asset = AVAsset(url: url)
let playerItem = AVPlayerItem(asset: asset)
let player = AVPlayer(playerItem: playerItem)

playerViewController.player = player
present(playerViewController, animated: true, completion: nil)

使用NSURLSession进行缓存
// 创建NSURLSessionConfiguration对象
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
// 设置缓存策略为NSURLRequestReturnCacheDataElseLoad
configuration.requestCachePolicy = NSURLRequestReturnCacheDataElseLoad;
// 创建NSURLSession对象
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];
// 创建NSURLRequest对象
NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://example.com/video.mp4"]];
// 发起网络请求
NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    if (error) {
        NSLog(@"Error: %@", error);
    } else {
        // 将视频数据保存到本地缓存
        NSString *cachePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0];
        NSString *filePath = [cachePath stringByAppendingPathComponent:@"video.mp4"];
        [data writeToFile:filePath atomically:YES];
        // 播放视频
        AVPlayerViewController *playerViewController = [[AVPlayerViewController alloc] init];
        playerViewController.player = [AVPlayer playerWithURL:[NSURL fileURLWithPath:filePath]];
        [self presentViewController:playerViewController animated:YES completion:nil];
    }
}];
[task resume];

// 创建AVAsset对象
AVAsset *asset = [AVAsset assetWithURL:[NSURL URLWithString:@"http://example.com/video.mp4"]];
// 创建AVAssetDownloadURLSessionConfiguration对象
AVAssetDownloadURLSessionConfiguration *configuration = [AVAssetDownloadURLSessionConfiguration new];
configuration.maximumActiveDownloads = 1;
configuration.allowsCellularAccess = NO;
// 设置缓存路径为Caches目录下的VideoCache文件夹
NSString *cachePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *cacheFolder = [cachePath stringByAppendingPathComponent:@"VideoCache"];
NSURL *cacheURL = [NSURL fileURLWithPath:cacheFolder isDirectory:YES];
configuration.destinationURL = cacheURL;
// 创建AVAssetDownloadURLSession对象
AVAssetDownloadURLSession *session = [AVAssetDownloadURLSession sessionWithConfiguration:configuration assetDownloadDelegate:self delegateQueue:nil];
// 创建AVAssetDownloadTask对象
AVAssetDownloadTask *task = [session assetDownloadTaskWithURLAsset:asset assetTitle:@"video" assetArtworkData:nil options:nil];
// 启动下载任务
[task resume];



在AVAssetDownloadDelegate协议方法中，做视频播放
当下载完成时，保存视频文件的本地路径，并使用AVPlayerViewController进行播放：
- (void)URLSession:(NSURLSession *)session assetDownloadTask:(AVAssetDownloadTask *)assetDownloadTask didFinishDownloadingToURL:(NSURL *)location {
    // 将视频数据保存到本地缓存
    NSString *cachePath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0

import UIKit
import AVFoundation
import AVKit

class ViewController: UIViewController {
    
    var player: AVPlayer!
    var playerLayer: AVPlayerLayer!

    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建AVPlayer
        // 这个M3U8文件包含了所有视频文件的URL地址，AVPlayer会根据这些URL逐一请求视频文件并进行播放。
        let url = URL(string: "http://example.com/video.m3u8")!
        player = AVPlayer(url: url)
        
        // 创建AVPlayerLayer
        playerLayer = AVPlayerLayer(player: player)
        playerLayer.frame = view.bounds
        view.layer.addSublayer(playerLayer)
        
        // 播放视频
        player.play()
    }
    
    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        
        // 调整AVPlayerLayer的大小
        playerLayer.frame = view.bounds
    }
}

// 播放/暂停视频
if player?.rate == 0 {
    player?.play()
} else {
    player?.pause()
}

//快进/快退视频：
let seekTime = CMTimeMakeWithSeconds(10.0, preferredTimescale: CMTimeScale(NSEC_PER_SEC))
let currentTime = player?.currentTime()
let targetTime = CMTimeAdd(currentTime!, seekTime)

player?.seek(to: targetTime)

//播放状态发生变化时的回调函数
player?.addPeriodicTimeObserver(forInterval: CMTimeMakeWithSeconds(1, preferredTimescale: CMTimeScale(NSEC_PER_SEC)), queue: DispatchQueue.main, using: { [weak self] (time) in
    // 更新播放进度
})

//播放器状态发生变化时的回调函数
player?.addObserver(self, forKeyPath: "status", options: [.old, .new], context: nil)

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if keyPath == "status" {
        if player?.status == .failed {
            // 播放失败
        } else if player?.status == .readyToPlay {
            // 准备播放
        }
    }
}