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七.音视频编辑-创建视频过渡-应用

news 2025/8/5 7:30:31

引言

在上一篇博客中，我们已经介绍了创建视频过渡的实现方案，步骤非常繁琐，在生成AVMutableVideoCompositionInstruction和AVMutableVideoCompositionLayerInstruction的计算也十分复杂，但其实还有一个创建视频组合的捷径。不过我们还是需要理解上一篇博客中我们所讨论的步骤，只有理解了那些步骤，才能发现学习这些对应的使用变得容易许多。

创建组合的捷径

AVVideoComposition定义了一个十分便捷的初始化方法init(propertiesOf asset: AVAsset)，我们可以将AVCompostion作为参数来创建一个AVVideoComposition。该方法会为我们创建一个带有如下配置的AVVideoComposition对象：

instructions 属性包含一组完整的基于组合视频轨道（以及其中包含的片段空间布局）的组合和层指令。
renderSize 属性被设置为AVComposition对象的naturalSize，或者如果没有设置，则使用能够满足组合视频轨道中最大视频维度的尺寸值。
frameDuration 设置为组合视频轨道中最大nominalFrameRate的值。如果所有轨道的nominalFrameRate值都为0，则frameDuration设置成默认1/30秒（30FPS）。
renderScale 始终设置为1.0。

创建视频过渡

下面我们开始着手创建视频过渡，和之前的实现方案一样，先创建一个遵循PHComposition协议名为PHTransitionComposition的类，以及遵循PHCompositionBuilder协议名为PHTransitionCompositionBuilder的类。

PHTransitionComposition负责构建视频的可播放和可导出版本。

PHTransitionCompositionBuilder负责构建PHTransitionComposition，里面会创建用于视频编辑的AVMutableComposition，AVMutableAudioMix以及AVMutableVideoComposition。

PHTransitionComposition

代码实现如下：

import UIKit
import AVFoundationclass PHTransitionComposition: NSObject,PHComposition {/// 组合轨道var composition:AVMutableComposition!/// 视频轨道var videoComposition:AVMutableVideoComposition?/// 音频混合var audioMix:AVMutableAudioMix?init(composition: AVMutableComposition!, videoComposition: AVMutableVideoComposition?, audioMix: AVMutableAudioMix?) {self.composition = compositionself.videoComposition = videoCompositionself.audioMix = audioMix}func makePlayerItem() -> AVPlayerItem? {let playerItem = AVPlayerItem(asset: composition.copy() as! AVAsset)playerItem.videoComposition = videoCompositionplayerItem.audioMix = audioMixreturn playerItem}func makeAssetExportSession() -> AVAssetExportSession? {let exportSession = AVAssetExportSession(asset: composition.copy() as! AVAsset, presetName: AVAssetExportPresetHighestQuality)exportSession?.videoComposition = videoCompositionexportSession?.audioMix = audioMixreturn exportSession!}}

代码较以前的类相比多了一个AVMutableVideoComposition属性，用来实现视频的过渡效果。

PHTransitionCompositionBuilder

该类中的代码和以往一样主要目的是构建PHComposition，分成三个部分，添加视频到组合轨道，添加音频到组合轨道，添加背景音乐到组合轨道。

let defaultTransitionDuration = CMTime(value: 2, timescale: 1)class PHTransitionCompositionBuilder: NSObject,PHCompositionBuilder {/// 资源模型var timeLine:PHTimeLine!/// 组合轨道let composition = AVMutableComposition()init(timeLine: PHTimeLine!) {self.timeLine = timeLine}func buildComposition() -> PHComposition? {// 添加视频到组合轨道addVideoCompositionTrack()// 创建AVVideoCompositionlet videoComposition = buildVideoComposition()// 添加音频到组合轨道addAudioCompositionTrack()// 添加背景音乐到组合轨道let audioMix = addMusicCompositionTrack()return PHTransitionComposition(composition: composition, videoComposition: videoComposition, audioMix: audioMix)}/// 添加视频到组合轨道func addVideoCompositionTrack() {....}/// 创建AVVideoCompositionfunc buildVideoComposition() -> AVMutableVideoComposition? {....}/// 添加音频到组合轨道func addAudioCompositionTrack() {let _ = addCompositionTrack(mediaType: .audio, mediaItems: timeLine.audioItems)}/// 添加背景音乐到组合轨道func addMusicCompositionTrack() -> AVMutableAudioMix?{// 添加背景音乐var audioMix:AVMutableAudioMix? = nilif timeLine.musicItem != nil {let musicCompositionTrack =  addCompositionTrack(mediaType: .audio, mediaItems: [timeLine.musicItem!])let musicAudioMix = buildAudioMixWithTrack(track: musicCompositionTrack)audioMix = musicAudioMix}return audioMix}/// 私有方法-添加媒体资源轨道/// - Parameters:///  - mediaType: 媒体类型///  - mediaItems: 媒体媒体资源数组///  - Returns: 返回一个AVCompositionTrackprivate func addCompositionTrack(mediaType:AVMediaType,mediaItems:[PHMediaItem]?) -> AVMutableCompositionTrack? {if PHIsEmpty(array: mediaItems) {return nil}let trackID = kCMPersistentTrackID_Invalidguard let compositionTrack = composition.addMutableTrack(withMediaType: mediaType, preferredTrackID: trackID) else { return nil }//设置起始时间var cursorTime = CMTime.zeroguard let mediaItems = mediaItems else { return nil }for item in mediaItems {//这里默认时间都是从0开始guard let asset = item.asset else { continue }guard let assetTrack = asset.tracks(withMediaType: mediaType).first  else { continue }do {try compositionTrack.insertTimeRange(item.timeRange, of: assetTrack, at: cursorTime)} catch {print("addCompositionTrack error")}cursorTime = CMTimeAdd(cursorTime, item.timeRange.duration)}return compositionTrack}/// 创建音频混合器/// - Parameters:///  - musicTrack: 音乐轨道func buildAudioMixWithTrack(track:AVMutableCompositionTrack?) -> AVMutableAudioMix? {guard let track = track else { return nil }guard let musicItem = timeLine.musicItem else { return nil }let audioMix = AVMutableAudioMix()let audioMixParam = AVMutableAudioMixInputParameters(track: track)for volumeAutomaition in musicItem.volumeAutomations {audioMixParam.setVolumeRamp(fromStartVolume: volumeAutomaition.startVolume, toEndVolume: volumeAutomaition.endVolume, timeRange: volumeAutomaition.timeRange)}audioMix.inputParameters = [audioMixParam]return audioMix}}

关于添加音频和背景音乐以及创建AVAudioMix的部分，我们在前面的博客中已经进行过介绍，在这里就不再重复解释了，把重点放到添加视频到组合轨道以及创建AVVideoComposition上。

下面看一下添加视频到组合轨道的实现：

    /// 添加视频到组合轨道func addVideoCompositionTrack() {let compositionTrackA = self.composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)let compositionTrackB = self.composition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)let videoTracks = [compositionTrackA,compositionTrackB]let transitionDuration = defaultTransitionDuration// 初始时间var cursorTime = CMTime.zerolet videoItems = timeLine.videoItmesfor (index,item) in videoItems.enumerated() {let trackIndex = index % 2let currentTrack = videoTracks[trackIndex]guard let asset = item.asset else { continue }guard let assetTrack = asset.tracks(withMediaType: .video).first else { continue }do {try currentTrack?.insertTimeRange(item.timeRange, of: assetTrack, at: cursorTime) } catch {print("insertTimeRange error")}// 更新cursorTimecursorTime = CMTimeAdd(cursorTime, item.timeRange.duration)cursorTime = CMTimeSubtract(cursorTime, transitionDuration)}}

首先从当前的AVMutableComposition中创建两个新的AVMutableCompositionTrack对象，两者都是.video类型，并添加到videoTracks数组中，提供所需的A-B轨道排列。
遍历视频资源，将视频资源交替插入到AB两个轨道中。
计算cursorTime，需要考虑到减去动画过程的时间，因为这段时间两个视频媒体是重叠的。

创建AVVideoComposition的实现如下：

    /// 创建AVVideoCompositionfunc buildVideoComposition() -> AVMutableVideoComposition? {let videoComposition = AVMutableVideoComposition(propertiesOf: self.composition)videoComposition.renderSize = CGSize(width: 1920, height: 1080)/// 获取instructionslet instructions = videoComposition.instructionsvar layerInstructionIndex = 1for instruction in instructions {guard let videoCompositionInstruction = instruction as? AVMutableVideoCompositionInstruction else { continue }let layerInstructions = videoCompositionInstruction.layerInstructions// 判断是否有两个layerInstructionsguard layerInstructions.count == 2 else { continue }// 创建过渡效果let fromeLayerInstruction = layerInstructions[1 - layerInstructionIndex] as! AVMutableVideoCompositionLayerInstructionlet toLayerInstruction = layerInstructions[layerInstructionIndex] as! AVMutableVideoCompositionLayerInstruction// 设置动画fromeLayerInstruction.setOpacityRamp(fromStartOpacity: 1.0, toEndOpacity: 0.0, timeRange: videoCompositionInstruction.timeRange)layerInstructionIndex = layerInstructionIndex == 1 ? 0 : 1}return videoComposition}

使用init(propertiesOf asset: AVAsset)创建一个新的AVVideoComposition实例，这个方法会自动创建所需的组合对象和层指令。并设置renderSize、renderScale、frameDuration熟悉为相应的值。（renderSize需要满足组合视频轨道中最大视频维度的尺寸值）
遍历videoComposition的instructions属性，判断videoCompositionInstruction的layerInstructions个数等于2的情况提取重叠的两个AVMutableVideoCompositionLayerInstruction。
为两个AVMutableVideoCompositionLayerInstruction添加一个渐变的过渡动画。
返回AVVideoComposition实例。

除了上面列出的最简单的渐隐过渡方式，还支持很多其它的过渡方式。

推入过渡效果：

            // 推入过渡效果let identityTransform = CGAffineTransform.identitylet videoWidth = videoComposition.renderSize.widthlet fromeTransform = CGAffineTransform(translationX: -videoWidth, y: 0)let toTransform = CGAffineTransform(translationX: videoWidth, y: 0)fromeLayerInstruction.setTransformRamp(fromStart: identityTransform, toEnd: fromeTransform, timeRange: videoCompositionInstruction.timeRange)toLayerInstruction.setTransformRamp(fromStart: toTransform, toEnd: identityTransform, timeRange: videoCompositionInstruction.timeRange)

擦除过渡效果：

            // 擦除过渡效果let width = videoComposition.renderSize.widthlet height = videoComposition.renderSize.heightlet startRect = CGRect(x: 0, y: 0, width: width, height: height)let endRect = CGRect(x: width, y: height, width: width, height: 0.0)fromeLayerInstruction.setCropRectangleRamp(fromStartCropRectangle: startRect, toEndCropRectangle: endRect, timeRange: videoCompositionInstruction.timeRange)

播放

创建PHTransitionCompositionBuilder实例，构建视频的可播放版本，进行播放。

 func player() {guard let delegate = self.delegate else { return }let compositionBuilder = PHTransitionCompositionBuilder(timeLine: timeLine)let composition = compositionBuilder.buildComposition()let playerItem = composition?.makePlayerItem()delegate.replaceCurrentItem(playerItem: playerItem)}