AVFoundation + AssetWriter：用图像和音频生成电影

电影

使用AVFoundation和AssetWriter可以很方便地将图像和音频合成为电影。这种方法非常适合需要动态生成电影的应用，比如实时视频编辑、视频特效等。

在这篇文章中，我们将介绍如何使用AVFoundation和AssetWriter来生成电影。我们将首先讨论如何准备图像和音频数据，然后介绍如何将它们合成为电影。

准备图像数据

在生成电影之前，我们需要准备好图像数据。首先，我们需要将图像转换为CMSampleBufferRef格式，这是AVFoundation中表示图像数据的一种方式。我们可以使用AVAssetWriterInputPixelBufferAdaptor来将图像数据写入到AssetWriter中。

以下是一个示例代码，演示了如何将UIImage转换为CMSampleBufferRef：

Swift
func createSampleBuffer(from image: UIImage) -> CMSampleBuffer? {
    let pixelBuffer = createPixelBuffer(from: image)
    
    var sampleTimingInfo = CMSampleTimingInfo(duration: CMTime(value: 1, timescale: 30), presentationTimeStamp: .zero, decodeTimeStamp: .invalid)
    
    var sampleBuffer: CMSampleBuffer?
    CMSampleBufferCreateForImageBuffer(allocator: kCFAllocatorDefault, imageBuffer: pixelBuffer, dataReady: true, makeDataReadyCallback: nil, refcon: nil, formatDescription: nil, sampleTiming: &sampleTimingInfo, sampleBufferOut: &sampleBuffer)
    
    return sampleBuffer
}
func createPixelBuffer(from image: UIImage) -> CVPixelBuffer? {
    let options: [String: Any] = [
        kCVPixelBufferCGImageCompatibilityKey as String: true,
        kCVPixelBufferCGBitmapContextCompatibilityKey as String: true
    ]
    
    var pixelBuffer: CVPixelBuffer?
    CVPixelBufferCreate(kCFAllocatorDefault, Int(image.size.width), Int(image.size.height), kCVPixelFormatType_32ARGB, options as CFDictionary, &pixelBuffer)
    
    if let pixelBuffer = pixelBuffer {
        CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        let context = CGContext(data: CVPixelBufferGetBaseAddress(pixelBuffer), width: Int(image.size.width), height: Int(image.size.height), bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer), space: CGColorSpaceCreateDeviceRGB(), bitmapInfo: CGImageAlphAInfo.premultipliedFirst.rawValue)
        context?.draw(image.cgImage!, in: CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height))
        CVPixelBufferUnlockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        
        return pixelBuffer
    }
    
    return nil
}

准备音频数据

除了图像数据，我们还需要准备音频数据。与图像数据类似，我们需要将音频数据转换为CMSampleBufferRef格式，并使用AVAssetWriterInput将其写入到AssetWriter中。

以下是一个示例代码，演示了如何将音频数据转换为CMSampleBufferRef：

Swift
func createSampleBuffer(from audioData: Data) -> CMSampleBuffer? {
    var sampleBuffer: CMSampleBuffer?
    
    var status = noErr
    
    var audioBufferList = AudioBufferList()
    audioBufferList.mNumberBuffers = 1
    audioBufferList.mBuffers.mNumberChannels = 1
    audioBufferList.mBuffers.mDataByteSize = UInt32(audioData.count)
    audioBufferList.mBuffers.mData = UnsafeMutableRawPointer(mutating: audioData.bytes)
    
    var format = AudIOStreamBasicDescription()
    format.mSampleRate = 44100
    format.mFormatID = kAudioFormatLinearPCM
    format.mFormatFlags = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked
    format.mFramesPerPacket = 1
    format.mChannelsPerFrame = 1
    format.mBitsPerChannel = 16
    format.mBytesPerFrame = format.mChannelsPerFrame * format.mBitsPerChannel / 8
    format.mBytesPerPacket = format.mFramesPerPacket * format.mBytesPerFrame
    
    var audioBuffer = AudioBuffer(mNumberChannels: format.mChannelsPerFrame, mDataByteSize: UInt32(audioData.count), mData: audioData.bytes)
    
    let bufferListSize = MemoryLayout<AudioBufferList>.size - MemoryLayout<AudioBuffer>.size + MemoryLayout<AudioBuffer>.size * Int(format.mChannelsPerFrame)
    let bufferList = UnsafeMutablePointer<AudioBufferList>.allocate(capacity: bufferListSize)
    bufferList.pointee = audioBufferList
    
    status = CMAudIOSampleBufferCreateReadyWithPacketDescriptions(allocator: kCFAllocatorDefault, dataBuffer: nil, formatDescription: nil, sampleCount: audioData.count / Int(format.mBytesPerPacket), presentationTimeStamp: .zero, packetDescriptions: nil, sampleBufferOut: &sampleBuffer)
    
    return sampleBuffer
}

生成电影

当我们准备好图像和音频数据后，我们可以开始生成电影了。首先，我们需要创建一个AVAssetWriter实例，并添加一个AVAssetWriterInput用于写入图像数据。然后，我们需要添加一个AVAssetWriterInput用于写入音频数据。

以下是一个示例代码，演示了如何生成电影：

Swift
func generateMovie(imageURLs: [URL], audioURL: URL, outputURL: URL) {
    let assetWriter = try! AVAssetWriter(outputURL: outputURL, fileType: .mov)
    
    let vIDEOSettings = [
        AVVIDEOCodecKey: AVVIDEOCodecType.h264,
        AVVIDEOWidthKey: 640,
        AVVIDEOHeightKey: 480
    ] as [String: Any]
    let vIDEOWriterInput = AVAssetWriterInput(mediaType: .vIDEO, outputSettings: vIDEOSettings)
    assetWriter.add(vIDEOWriterInput)
    
    let audIOSettings = [
        AVFormatIDKey: kAudioFormatLinearPCM,
        AVSampleRateKey: 44100,
        AVNumberOfChannelsKey: 1,
        AVLinearPCMBitDepthKey: 16,
        AVLinearPCMIsNonInterleaved: false,
        AVLinearPCMIsFloatKey: false,
        AVLinearPCMIsBigEndianKey: false
    ] as [String: Any]
    let audioWriterInput = AVAssetWriterInput(mediaType: .audio, outputSettings: audIOSettings)
    assetWriter.add(audioWriterInput)
    
    assetWriter.startWriting()
    assetWriter.startSession(atSourceTime: .zero)
    
    let vIDEOQueue = DispatchQueue(label: "vIDEOQueue")
    let audioQueue = DispatchQueue(label: "audioQueue")
    
    vIDEOWriterInput.requestMediaDataWhenReady(on: vIDEOQueue) {
        while vIDEOWriterInput.isReadyForMoreMediaData {
            if let imageURL = imageURLs.first {
                imageURLs.removeFirst()
                
                let image = UIImage(contentsOfFile: imageURL.path)!
                let sampleBuffer = createSampleBuffer(from: image)!
                
                vIDEOWriterInput.append(sampleBuffer)
            } else {
                vIDEOWriterInput.markAsFinished()
                break
            }
        }
    }
    
    audioWriterInput.requestMediaDataWhenReady(on: audioQueue) {
        while audioWriterInput.isReadyForMoreMediaData {
            if let audioData = try? Data(contentsOf: audioURL) {
                let sampleBuffer = createSampleBuffer(from: audioData)!
                
                audioWriterInput.append(sampleBuffer)
            } else {
                audioWriterInput.markAsFinished()
                break
            }
        }
    }
    
    assetWriter.finishWriting {
        print("Movie generated successfully!")
    }
}

在这个示例代码中，我们首先创建了一个AVAssetWriter实例，并为视频设置了一些参数，比如编码格式和分辨率。然后，我们为音频设置了一些参数，比如采样率和声道数。接下来，我们使用两个队列来分别处理视频和音频数据。

在视频队列中，我们从图像URL数组中依次读取图像数据，并将其转换为CMSampleBufferRef格式，然后使用AVAssetWriterInput将其写入到AssetWriter中。

在音频队列中，我们从音频URL中读取音频数据，并将其转换为CMSampleBufferRef格式，然后使用AVAssetWriterInput将其写入到AssetWriter中。

当所有的数据都写入完成后，我们调用finishWriting方法来完成电影的生成。

使用AVFoundation和AssetWriter，我们可以很方便地将图像和音频合成为电影。在本文中，我们介绍了如何准备图像和音频数据，并使用AVAssetWriter将它们合成为电影。这种方法非常灵活，可以用于各种需要动态生成电影的应用场景。

案例代码

Swift
// 示例代码

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