Question

我正在考虑让我的Swift iOS应用程序录制视频并在同一屏幕上播放，延迟30秒。

我一直在使用official example录制视频。然后我添加了一个按钮，可以在屏幕上的单独视图中使用AVPlayer触发播放self.movieFileOutput?.outputFileURL。它接近我想要的但显然它一旦到达写入磁盘的文件的末尾就停止播放，并且在写入下一个缓冲的块时不会继续播放。

我可以每隔30秒停止一次视频录制并保存每个文件的URL，以便我可以播放它，但这意味着视频捕获和播放会中断。

如何让视频录制从不停止，播放始终在屏幕上，我想要任何延迟？

我已经看到了类似的问题，所有答案都指向AVFoundation docs。我无法找到如何让AVFoundation在录制时将可预测的视频块从内存写入磁盘。

Answer 1

您可以通过录制30个视频块然后将它们排入AVQueuePlayer进行无缝播放来实现您想要的效果。在macOS上使用AVCaptureFileOutput录制视频块非常容易，但遗憾的是，在iOS上，如果不丢帧，则无法创建新块，因此必须使用更低级别的AVAssetWriter API：

import UIKit
import AVFoundation

// TODO: delete old videos
// TODO: audio

class ViewController: UIViewController {
    // capture
    let captureSession = AVCaptureSession()

    // playback
    let player = AVQueuePlayer()
    var playerLayer: AVPlayerLayer! = nil

    // output. sadly not AVCaptureMovieFileOutput
    var assetWriter: AVAssetWriter! = nil
    var assetWriterInput: AVAssetWriterInput! = nil

    var chunkNumber = 0
    var chunkStartTime: CMTime! = nil
    var chunkOutputURL: URL! = nil

    override func viewDidLoad() {
        super.viewDidLoad()

        playerLayer = AVPlayerLayer(player: player)
        view.layer.addSublayer(playerLayer)

        // inputs
        let videoCaptureDevice = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
        let videoInput = try! AVCaptureDeviceInput(device: videoCaptureDevice)
        captureSession.addInput(videoInput)

        // outputs
        // iOS AVCaptureFileOutput/AVCaptureMovieFileOutput still don't support dynamically
        // switching files (?) so we have to re-implement with AVAssetWriter
        let videoOutput = AVCaptureVideoDataOutput()
        // TODO: probably something else
        videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue.main)
        captureSession.addOutput(videoOutput)

        captureSession.startRunning()
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        playerLayer.frame = view.layer.bounds
    }

    func createWriterInput(for presentationTimeStamp: CMTime) {
        let fileManager = FileManager.default
        chunkOutputURL = fileManager.urls(for: .documentDirectory, in: .userDomainMask)[0].appendingPathComponent("chunk\(chunkNumber).mov")
        try? fileManager.removeItem(at: chunkOutputURL)

        assetWriter = try! AVAssetWriter(outputURL: chunkOutputURL, fileType: AVFileTypeQuickTimeMovie)
        // TODO: get dimensions from image CMSampleBufferGetImageBuffer(sampleBuffer)
        let outputSettings: [String: Any] = [AVVideoCodecKey:AVVideoCodecH264, AVVideoWidthKey: 1920, AVVideoHeightKey: 1080]
        assetWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: outputSettings)
        assetWriterInput.expectsMediaDataInRealTime = true
        assetWriter.add(assetWriterInput)

        chunkNumber += 1
        chunkStartTime = presentationTimeStamp

        assetWriter.startWriting()
        assetWriter.startSession(atSourceTime: chunkStartTime)
    }
}

extension ViewController: AVCaptureVideoDataOutputSampleBufferDelegate {
    func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
        let presentationTimeStamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)

        if assetWriter == nil {
            createWriterInput(for: presentationTimeStamp)
        } else {
            let chunkDuration = CMTimeGetSeconds(CMTimeSubtract(presentationTimeStamp, chunkStartTime))

            if chunkDuration > 30 {
                assetWriter.endSession(atSourceTime: presentationTimeStamp)

                // make a copy, as finishWriting is asynchronous
                let newChunkURL = chunkOutputURL!
                let chunkAssetWriter = assetWriter!

                chunkAssetWriter.finishWriting {
                    print("finishWriting says: \(chunkAssetWriter.status.rawValue, chunkAssetWriter.error)")
                    print("queuing \(newChunkURL)")
                    self.player.insert(AVPlayerItem(url: newChunkURL), after: nil)
                    self.player.play()
                }
                createWriterInput(for: presentationTimeStamp)
            }
        }

        if !assetWriterInput.append(sampleBuffer) {
            print("append says NO: \(assetWriter.status.rawValue, assetWriter.error)")
        }
    }
}

P.S。 30秒前看到你在做什么真是太好奇了。你到底在做什么？

如何使用AVFoundation同时录制和播放捕获的视频，延迟几秒钟？

1 个答案: