使用帧逐帧方法制作带音频的慢动作视频 - iOS

要使用帧逐帧方法制作带音频的慢动作视频，您可以按照以下步骤进行操作：

1. 导入AVFoundation框架和AVKit框架：

import AVFoundation
import AVKit

2. 获取要处理的视频文件和音频文件的URL：

let videoURL = Bundle.main.url(forResource: "video", withExtension: "mp4")
let audioURL = Bundle.main.url(forResource: "audio", withExtension: "mp3")

3. 创建一个AVAsset对象来处理视频和音频：

let videoAsset = AVURLAsset(url: videoURL!)
let audioAsset = AVURLAsset(url: audioURL!)

4. 创建一个AVMutableComposition对象并将视频和音频添加到它：

let composition = AVMutableComposition()
let compositionVideoTrack = composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
let compositionAudioTrack = composition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)

let videoTrack = videoAsset.tracks(withMediaType: .video)[0]
let audioTrack = audioAsset.tracks(withMediaType: .audio)[0]

try! compositionVideoTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: videoAsset.duration), of: videoTrack, at: CMTime.zero)
try! compositionAudioTrack?.insertTimeRange(CMTimeRangeMake(start: CMTime.zero, duration: videoAsset.duration), of: audioTrack, at: CMTime.zero)

5. 创建一个AVMutableVideoComposition对象来处理慢动作效果，并设置时间缩放因子：

let videoComposition = AVMutableVideoComposition()
videoComposition.frameDuration = CMTimeMake(value: 1, timescale: 30) // 设置帧率为30fps
videoComposition.renderSize = videoTrack.naturalSize

let timeScaleFactor: Float64 = 0.5 // 设置慢动作倍速，这里是0.5，即放慢一倍
let timeRange = CMTimeRangeMake(start: CMTime.zero, duration: videoAsset.duration)

let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: compositionVideoTrack!)
videoLayerInstruction.setTransform(videoTrack.preferredTransform, at: CMTime.zero)
videoLayerInstruction.setOpacity(0.0, at: videoAsset.duration)

videoComposition.instructions = [AVMutableVideoCompositionInstruction]()
let videoCompositionInstruction = AVMutableVideoCompositionInstruction()
videoCompositionInstruction.timeRange = timeRange
videoCompositionInstruction.layerInstructions = [videoLayerInstruction]

videoComposition.instructions.append(videoCompositionInstruction)

6. 创建一个AVMutableAudioMix对象来处理音频：

let audioMix = AVMutableAudioMix()
let audioMixInputParameters = AVMutableAudioMixInputParameters(track: compositionAudioTrack)
audioMixInputParameters.setVolumeRamp(fromStartVolume: 1.0, toEndVolume: 1.0, timeRange: timeRange)
audioMix.inputParameters = [audioMixInputParameters]

7. 创建一个AVPlayerItem对象并将其与AVPlayer关联：

let playerItem = AVPlayerItem(asset: composition)
playerItem.videoComposition = videoComposition
playerItem.audioMix = audioMix

let player = AVPlayer(playerItem: playerItem)

8. 创建一个AVPlayerViewController对象并将其与AVPlayer关联：

let playerViewController = AVPlayerViewController()
playerViewController.player = player

9. 在视图中显示AVPlayerViewController：

self.present(playerViewController, animated: true) {
    playerViewController.player?.play()
}

这是一个基本的示例，可以根据您的需求进行进一步的定制和调整。