ios - CGBitmapContext和CVPixelBuffer的视频输出失真

Question

我一直在尝试调试该代码(现在已经几天了)，以从CGImages产生视频。 CGImage实际上是从我在应用程序代码中绘制的CGBitMapContext的创建的。在这里，我已简化为仅画一条对角的黄线并绘制该静态图像的许多帧。但是，这是我在写入路径中发现的失真视频的一个帧(每个帧都是相同的)。

import Foundation
import CoreGraphics
import CoreMedia
import QuartzCore
import AVFoundation

func exportVideo(
    width: Int = 500,
    height: Int = 500,
    numberOfFrames: Int = 100
) {
    let vidURL = NSURL.fileURL(withPath: "/Users/me/Desktop/testVideo.mp4")

    try? FileManager.default.removeItem(at: vidURL)

    let settings: [String: Any] = [
        AVVideoCodecKey: AVVideoCodecType.h264,
        AVVideoWidthKey: width,
        AVVideoHeightKey: height
    ]

    let assetWriter = try! AVAssetWriter(url: vidURL, fileType: .m4v)
    let writerInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: settings)
    assetWriter.add(writerInput)

    let queue = DispatchQueue.global(qos: .background)

    writerInput.expectsMediaDataInRealTime = false

    let inputAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: writerInput, sourcePixelBufferAttributes: nil)

    assetWriter.startWriting()

    assetWriter.startSession(atSourceTime: CMTime.zero)

    writerInput.requestMediaDataWhenReady(on: queue) {

        for i in 0..<numberOfFrames where writerInput.isReadyForMoreMediaData {

            guard let buffer = newPixelBufferFrom(width: width, height: height) else {
                fatalError()
            }

            inputAdaptor.append(
                buffer,
                withPresentationTime: CMTime(seconds: Double(i), preferredTimescale: CMTimeScale(10))
            )
        }

        writerInput.markAsFinished()

        assetWriter.finishWriting { }
    }
}

private func newPixelBufferFrom(
    width: Int,
    height: Int
) -> CVPixelBuffer? {

    let options:[String: Any] = [
        kCVPixelBufferCGImageCompatibilityKey as String: true,
        kCVPixelBufferCGBitmapContextCompatibilityKey as String: true
    ]

    var pxbuffer: CVPixelBuffer?
    let status = CVPixelBufferCreate(kCFAllocatorDefault,
                                     width,
                                     height,
                                     kCVPixelFormatType_32ARGB,
                                     options as CFDictionary?,
                                     &pxbuffer)

    assert(status == kCVReturnSuccess && pxbuffer != nil, "newPixelBuffer failed")

    CVPixelBufferLockBaseAddress(pxbuffer!, CVPixelBufferLockFlags(rawValue: 0))

    let pxdata = CVPixelBufferGetBaseAddress(pxbuffer!)

    let rgbColorSpace = CGColorSpaceCreateDeviceRGB()

    guard let context = CGContext(
        data: pxdata,
        width: width,
        height: height,
        bitsPerComponent: 8,
        bytesPerRow: 4 * width,
        space: rgbColorSpace,
        bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue
        ) else {
            fatalError()
    }

    context.setStrokeColor(UIColor.yellow.cgColor)
    context.setLineWidth(5)
    context.move(to: .init(x: 0, y: 0))
    context.addLine(to: .init(x: width, y: height))
    context.strokePath()

    CVPixelBufferUnlockBaseAddress(pxbuffer!, CVPixelBufferLockFlags(rawValue: 0))
    return pxbuffer
}

Answer 1

所以我偶然发现了我的问题here的“答案”。

事实证明，宽度和高度必须是4的倍数。我只想说，我希望这篇文章对将来可怜的人有所帮助，因为错误代码，警告，API成员和文档完全无法帮助我。