iOS-显示hdr-视频-写出详细代码

由于 iOS 平台的硬件限制，在显示 HDR 视频时需要使用 Metal 库来进行硬件加速。以下是一个基本的示例代码，展示了如何使用 AVFoundation 和 Metal 库来显示 HDR 视频。

首先，需要导入必要的框架：

import AVFoundation
import Metal
import MetalKit

然后创建 AVPlayerItem 实例，并将其与 AVPlayer 相关联：

let playerItem = AVPlayerItem(url: videoURL)
let player = AVPlayer(playerItem: playerItem)

接下来，创建一个 AVPlayerLayer 的实例，并将其添加到视图中：

let playerLayer = AVPlayerLayer(player: player)
playerLayer.frame = view.bounds
view.layer.addSublayer(playerLayer)

然后，创建一个 MTKView 的实例，用于渲染视频帧：

let metalView = MTKView(frame: view.bounds, device: MTLCreateSystemDefaultDevice())
metalView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
view.addSubview(metalView)

接下来，创建一个 AVPlayerItemVideoOutput 实例，并使用它来检索视频帧：

let itemVideoOutput = AVPlayerItemVideoOutput(pixelBufferAttributes: [kCVPixelBufferMetalCompatibilityKey as String: true])
playerItem.add(itemVideoOutput)
let queue = DispatchQueue(label: "videoOutputQueue")
itemVideoOutput.setDelegate(self, queue: queue)

然后，实现 AVPlayerItemOutputPullDelegate 协议中的方法，处理每一帧视频：

func outputMediaDataWillChange(_ sender: AVPlayerItemOutput) {
    // Start rendering
}

func outputSequenceWasFlushed(_ output: AVPlayerItemOutput) {
    // Flush rendering
}

func output(_ output: AVPlayerItemOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVAssetReadaudioMixOutputngInspectionConnection) {
    guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
        return
    }
    
    // Convert pixel buffer to Metal texture
    let textureLoader = MTKTextureLoader(device: metalView.device!)
    let texture = try! textureLoader.newTexture(with: pixelBuffer, options: nil)
    
    // Render texture to Metal view
    let commandQueue = metalView.device!.makeCommandQueue()!
    let commandBuffer = commandQueue.makeCommandBuffer()!
    let renderPassDescriptor = metalView.currentRenderPassDescriptor!
    let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor)!
    renderEncoder.setRenderPipelineState(renderPipelineState)
    renderEncoder.setVertexBuffer(vertexBuffer, offset: 0, index: 0)
    renderEncoder.setFragmentTexture(texture, index: 0)
    renderEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 6)
    renderEncoder.endEncoding()
    commandBuffer.present(metalView.currentDrawable!)
    commandBuffer.commit()
}

最后，创建一个 Metal 渲染管道，用于将视频帧渲染到屏幕上：

let defaultLibrary = metalView.device!.makeDefaultLibrary()!
let vertexFunction = defaultLibrary.makeFunction(name: "vertexShader")
let fragmentFunction = defaultLibrary.makeFunction(name: "fragmentShader")
let renderPipelineDescriptor = MTLRenderPipelineDescriptor()
renderPipelineDescriptor.vertexFunction = vertexFunction
renderPipelineDescriptor.fragmentFunction = fragmentFunction
renderPipelineDescriptor.colorAttachments[0].pixelFormat = metalView.colorPixelFormat
let renderPipelineState = try! metalView.device!.makeRenderPipelineState(descriptor: renderPipelineDescriptor)

完整的代码示例：

import AVFoundation
import Metal
import MetalKit

class ViewController: UIViewController, AVPlayerItemOutputPullDelegate {
    var player: AVPlayer!
    var playerLayer: AVPlayerLayer!
    var metalView: MTKView!
    var renderPipelineState: MTLRenderPipelineState!
    var vertexBuffer: MTLBuffer!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let videoURL = Bundle.main.url(forResource: "video", withExtension: "mp4")!
        
        let playerItem = AVPlayerItem(url: videoURL)
        player = AVPlayer(playerItem: playerItem)
        
        playerLayer = AVPlayerLayer(player: player)
        playerLayer.frame = view.bounds
        view.layer.addSublayer(playerLayer)
        
        metalView = MTKView(frame: view.bounds, device: MTLCreateSystemDefaultDevice())
        metalView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        view.addSubview(metalView)
        
        let defaultLibrary = metalView.device!.makeDefaultLibrary()!
        let vertexFunction = defaultLibrary.makeFunction(name: "vertexShader")
        let fragmentFunction = defaultLibrary.makeFunction(name: "fragmentShader")
        let renderPipelineDescriptor = MTLRenderPipelineDescriptor()
        renderPipelineDescriptor.vertexFunction = vertexFunction
        renderPipelineDescriptor.fragmentFunction = fragmentFunction
        renderPipelineDescriptor.colorAttachments[0].pixelFormat = metalView.colorPixelFormat
        renderPipelineState = try! metalView.device!.makeRenderPipelineState(descriptor: renderPipelineDescriptor)
        
        let vertices: [Float] = [
            -1.0, -1.0, 0.0, 1.0,
            1.0, -1.0, 0.0, 1.0,
            -1.0,  1.0, 0.0, 1.0,
            1.0,  1.0, 0.0, 1.0
        ]
        vertexBuffer = metalView.device!.makeBuffer(bytes: vertices, length: vertices.count * MemoryLayout<Float>.size, options: [])
        
        let itemVideoOutput = AVPlayerItemVideoOutput(pixelBufferAttributes: [kCVPixelBufferMetalCompatibilityKey as String: true])
        playerItem.add(itemVideoOutput)
        let queue = DispatchQueue(label: "videoOutputQueue")
        itemVideoOutput.setDelegate(self, queue: queue)
        
        player.play()
    }
    
    func outputMediaDataWillChange(_ sender: AVPlayerItemOutput) {
        // Start rendering
    }
    
    func outputSequenceWasFlushed(_ output: AVPlayerItemOutput) {
        // Flush rendering
    }
    
    func output(_ output: AVPlayerItemOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVAssetReadaudioMixOutputngInspectionConnection) {
        guard let pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else {
            return
        }
        
        // Convert pixel buffer to Metal texture
        let textureLoader = MTKTextureLoader(device: metalView.device!)
        let texture = try! textureLoader.newTexture(with: pixelBuffer, options: nil)
        
        // Render texture to Metal view
        let commandQueue = metalView.device!.makeCommandQueue()!
        let commandBuffer = commandQueue.makeCommandBuffer()!
        let renderPassDescriptor = metalView.currentRenderPassDescriptor!
        let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor)!
        renderEncoder.setRenderPipelineState(renderPipelineState)
        renderEncoder.setVertexBuffer(vertexBuffer, offset: 0, index: 0)
        renderEncoder.setFragmentTexture(texture, index: 0)
        renderEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 6)
        renderEncoder.endEncoding()
        commandBuffer.present(metalView.currentDrawable!)
        commandBuffer.commit()
    }
}