me 学习MacOS App (Part 5: AVFoundation and system arch)

学习MacOS App (Part 5: AVFoundation and system arch)

Open nonocast opened this issue 3 years ago • 0 comments

MacOS和iOS的音视频框架主体都是围绕AVFoundation这个Framework，AVFoundation包括6个部分:

Assets
Playback
Capture
Editing
Audio
Speech

跟随Learning AV Foundation来看第一个hello world，直接新建一个swift playground

import AVFoundation

let synthesizer = AVSpeechSynthesizer()
let utterance = AVSpeechUtterance(string: "你好, 朋友。Nice to meet you.")
utterance.voice = AVSpeechSynthesisVoice(language: "zh-CN")
synthesizer.speak(utterance)

运行以后会很流畅说出中英文，换成稍微复杂的一些长句还是不太行，差不多就这样吧。

Video Player

官方教程: Creating a Basic Video Player (macOS) | Apple Developer Documentation

if let url = URL(string: "https://devstreaming-cdn.apple.com/videos/streaming/examples/img_bipbop_adv_example_ts/master.m3u8") {
    playerView.player = AVPlayer(url: url)
}

注:

如果是播放http的url，则需要关闭ATS，同时添加NSDomainException, 参考swift - AVPlayer won't let me access URL - Stack Overflow
本地文件：let url = URL(string: "file:///Users/nonocast/Movies/Teams.mp4")，但一定要注意file access的权限

Thumbnail

通过AVAsset我们来指向这个mp4，然后再来获取截图，

f let url = URL(string: "file:///Users/nonocast/Movies/Teams.mp4") {
    let asset = AVURLAsset(url: url)
    print("duration: \(String(format:"%.1f", CMTimeGetSeconds(asset.duration)))s")
    let assetSize =  asset.tracks(withMediaType: .video)[0].naturalSize
    print("resolution: \(assetSize)")
    
    // thumbnail
    let imageGen = AVAssetImageGenerator(asset: asset)
    imageGen.appliesPreferredTrackTransform = true
    
    do {
        let cgImage = try imageGen.copyCGImage(at: CMTimeMake(value: 20, timescale: 1), actualTime: nil)
        let image = NSImage(cgImage: cgImage, size: NSSize(width: cgImage.width, height: cgImage.height))
        imageView.image = image
    } catch {
        print(error.localizedDescription)
    }
}

具体参考: How to get thumbnail image from video URL in background swift

CALayer

如果你需要做个圆角裁切，这时你就需要用到CALayer

myView.wantsLayer = true
// myView.layer?.backgroundColor = NSColor.red.cgColor
myView.layer?.backgroundColor = NSColor(red: 1, green: 0, blue: 0, alpha: 0.3).cgColor
myView.layer?.cornerRadius = 15

然后你就会发现UIView只是一个抽象，绘图真正是通过CALayer，即Core Animation，通过Core Graphics，最终由Quartz2D进行绘制。这里就需要简单了解一下整个显示架构：