使CIContext.Render(CIImage，CVPixelBuffer)使用AVAssetWriter

本文介绍了使CIContext.Render(CIImage，CVPixelBuffer)使用AVAssetWriter的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我要使用Core Image处理一组CGImage对象，并在MacOS上将它们转换为QuickTime电影。以下代码演示了所需的内容，但output contains a lot of blank (black) frames：

import AppKit
import AVFoundation
import CoreGraphics
import Foundation
import CoreVideo
import Metal

// Video output url.
let url: URL = try! FileManager.default.url(for: .downloadsDirectory, in: .userDomainMask, appropriateFor: nil, create: false).appendingPathComponent("av.mov")
try? FileManager.default.removeItem(at: url)

// Video frame size, total frame count, frame rate and frame image.
let frameSize: CGSize = CGSize(width: 2000, height: 1000)
let frameCount: Int = 100
let frameRate: Double = 1 / 30
let frameImage: CGImage

frameImage = NSImage(size: frameSize, flipped: false, drawingHandler: {
    NSColor.red.setFill()
    $0.fill()
    return true
}).cgImage(forProposedRect: nil, context: nil, hints: nil)!

let pixelBufferAttributes: [CFString: Any]
let outputSettings: [String: Any]

pixelBufferAttributes = [
    kCVPixelBufferPixelFormatTypeKey: Int(kCVPixelFormatType_32ARGB),
    kCVPixelBufferWidthKey: Float(frameSize.width),
    kCVPixelBufferHeightKey: Float(frameSize.height),
    kCVPixelBufferMetalCompatibilityKey: true,
    kCVPixelBufferCGImageCompatibilityKey: true,
    kCVPixelBufferCGBitmapContextCompatibilityKey: true,
]

outputSettings = [
    AVVideoCodecKey: AVVideoCodecType.h264,
    AVVideoWidthKey: Int(frameSize.width),
    AVVideoHeightKey: Int(frameSize.height),
]

let writer: AVAssetWriter = try! AVAssetWriter(outputURL: url, fileType: .mov)
let input: AVAssetWriterInput = AVAssetWriterInput(mediaType: .video, outputSettings: outputSettings)
let pixelBufferAdaptor: AVAssetWriterInputPixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: input, sourcePixelBufferAttributes: pixelBufferAttributes as [String: Any])

input.expectsMediaDataInRealTime = true

precondition(writer.canAdd(input))
writer.add(input)

precondition(writer.startWriting())
writer.startSession(atSourceTime: CMTime.zero)

let colorSpace: CGColorSpace = CGColorSpace(name: CGColorSpace.sRGB) ?? CGColorSpaceCreateDeviceRGB()
let context = CIContext(mtlDevice: MTLCreateSystemDefaultDevice()!)

Swift.print("Starting the render…")

// Preferred scenario: using CoreImage to fill the buffer from the pixel buffer adapter. Shows that
// CIImage + AVAssetWriterInputPixelBufferAdaptor are not working together.

for frameNumber in 0 ..< frameCount {
    var pixelBuffer: CVPixelBuffer?
    guard let pixelBufferPool: CVPixelBufferPool = pixelBufferAdaptor.pixelBufferPool else { preconditionFailure() }
    precondition(CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &pixelBuffer) == kCVReturnSuccess)

    precondition(CVPixelBufferLockBaseAddress(pixelBuffer!, []) == kCVReturnSuccess)
    defer { precondition(CVPixelBufferUnlockBaseAddress(pixelBuffer!, []) == kCVReturnSuccess) }

    let ciImage = CIImage(cgImage: frameImage)
    context.render(ciImage, to: pixelBuffer!)

    // 💥 This fails – the pixel buffer doesn't get filled. AT ALL! Why? How to make it work?
    let bytes = UnsafeBufferPointer(start: CVPixelBufferGetBaseAddress(pixelBuffer!)!.assumingMemoryBound(to: UInt8.self), count: CVPixelBufferGetDataSize(pixelBuffer!))
    precondition(bytes.contains(where: { $0 != 0 }))

    while !input.isReadyForMoreMediaData { Thread.sleep(forTimeInterval: 10 / 1000) }
    precondition(pixelBufferAdaptor.append(pixelBuffer!, withPresentationTime: CMTime(seconds: Double(frameNumber) * frameRate, preferredTimescale: 600)))
}


// Unpreferred scenario: using CoreImage to fill the manually created buffer. Proves that CIImage
// can fill buffer and working.

// for frameNumber in 0 ..< frameCount {
//     var pixelBuffer: CVPixelBuffer?
//     precondition(CVPixelBufferCreate(nil, frameImage.width, frameImage.height, kCVPixelFormatType_32ARGB, pixelBufferAttributes as CFDictionary, &pixelBuffer) == kCVReturnSuccess)
//
//     precondition(CVPixelBufferLockBaseAddress(pixelBuffer!, []) == kCVReturnSuccess)
//     defer { precondition(CVPixelBufferUnlockBaseAddress(pixelBuffer!, []) == kCVReturnSuccess) }
//
//     let ciImage = CIImage(cgImage: frameImage)
//     context.render(ciImage, to: pixelBuffer!)
//
//     // ✅ This passes.
//     let bytes = UnsafeBufferPointer(start: CVPixelBufferGetBaseAddress(pixelBuffer!)!.assumingMemoryBound(to: UInt8.self), count: CVPixelBufferGetDataSize(pixelBuffer!))
//     precondition(bytes.contains(where: { $0 != 0 }))
//
//     while !input.isReadyForMoreMediaData { Thread.sleep(forTimeInterval: 10 / 1000) }
//     precondition(pixelBufferAdaptor.append(pixelBuffer!, withPresentationTime: CMTime(seconds: Double(frameNumber) * frameRate, preferredTimescale: 600)))
// }


// Unpreferred scenario: using CoreGraphics to fill the buffer from the pixel buffer adapter. Shows that
// buffer from pixel buffer adapter can be filled and working.

// for frameNumber in 0 ..< frameCount {
//     var pixelBuffer: CVPixelBuffer?
//     guard let pixelBufferPool: CVPixelBufferPool = pixelBufferAdaptor.pixelBufferPool else { preconditionFailure() }
//     precondition(CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &pixelBuffer) == kCVReturnSuccess)
//
//     precondition(CVPixelBufferLockBaseAddress(pixelBuffer!, []) == kCVReturnSuccess)
//     defer { precondition(CVPixelBufferUnlockBaseAddress(pixelBuffer!, []) == kCVReturnSuccess) }
//
//     guard let context: CGContext = CGContext(data: CVPixelBufferGetBaseAddress(pixelBuffer!), width: frameImage.width, height: frameImage.height, bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer!), space: colorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue) else { preconditionFailure() }
//     context.clear(CGRect(origin: .zero, size: frameSize))
//     context.draw(frameImage, in: CGRect(origin: .zero, size: frameSize))
//
//     // ✅ This passes.
//     let bytes = UnsafeBufferPointer(start: CVPixelBufferGetBaseAddress(pixelBuffer!)!.assumingMemoryBound(to: UInt8.self), count: CVPixelBufferGetDataSize(pixelBuffer!))
//     precondition(bytes.contains(where: { $0 != 0 }))
//
//     while !input.isReadyForMoreMediaData { Thread.sleep(forTimeInterval: 10 / 1000) }
//     precondition(pixelBufferAdaptor.append(pixelBuffer!, withPresentationTime: CMTime(seconds: Double(frameNumber) * frameRate, preferredTimescale: 600)))
// }

let semaphore = DispatchSemaphore(value: 0)

input.markAsFinished()
writer.endSession(atSourceTime: CMTime(seconds: Double(frameCount) * frameRate, preferredTimescale: 600))
writer.finishWriting(completionHandler: { semaphore.signal() })

semaphore.wait()

Swift.print("Successfully finished rendering to (url.path)")

但是，以下内容适用于CGContext，但我需要CIContext才能使用GPU。问题似乎出在AVAssetWriterInputPixelBufferAdaptor的缓冲池提供的像素缓冲区上。将CIContext渲染到单独创建的缓冲区并将其附加到适配器上是可行的，但效率非常低。渲染CIContext到适配器的池提供的缓冲区会导致根本没有数据写入缓冲区，其字面意思是全零，就好像两个不兼容！但是，使用CGImage渲染是可行的，因此可以手动复制数据。<

主要观察到CIContext.render似乎异步工作，或者在填充缓冲区和将数据写入视频流之间出现问题。换句话说，当缓冲区被刷新时，缓冲区中没有数据。以下内容有点指向那个方向：

删除缓冲区锁定会导致几乎所有帧都被写入，除了前几个帧之外，上面的代码实际上会生成correct output，但对于实际数据，其行为如所述。
使用不同的编解码器(如ProRes422)会导致几乎所有帧都被正确写入，只有几个空白-此外，上面的代码也会生成correct output，但较大且复杂的图像会导致跳过帧。

此代码有什么问题，正确的操作方法是什么？

附注：大多数iOS示例使用几乎相同的实现，并且看起来工作得非常好。我发现一个hint对于MacOS可能有所不同，但看不到任何有关此问题的官方文档。

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使CIContext.Render(CIImage，CVPixelBuffer)使用AVAssetWriter

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