ios AVFoundation框架给视频添加背景音乐的方法

/// 视频添加背景音乐
    /// - Parameters:
    ///   - videoURL: 视频文件URL
    ///   - audioURL: 音频文件URL
    ///   - startTime: 音频开始时间
    ///   - endTime: 音频结束时间
    ///   - isOriginal: 是否保留视频原音
    ///   - oriVolume: 视频原音音量
    ///   - newVolume: 新增背景音乐音量
    ///   - outputURL: 视频输出文件地址
    ///   - completion: 完成回掉
    static func addBackgroundMusic(videoURL : URL, audioURL : URL, startTime : Double, endTime : Double, isOriginal : Bool = true, oriVolume : Float, newVolume : Float, outputURL : String, completion : @escaping (_ success : Bool) -> Void) {
        
        if FileManager.default.fileExists(atPath: outputURL) {
            do {
                try FileManager.default.removeItem(atPath: outputURL)
            } catch {
                logger(item: "addBackgroundMusic remove exit file error")
            }
        }
        
        do {
            //导出路径
            let outputFileURL = URL.init(fileURLWithPath: outputURL)
            
            let nextClipStartTime = CMTime.zero
            
            //创建可变的音频视频组合
            let mixComposition = AVMutableComposition()
            
            //视频采集
            let videoAsset = AVURLAsset.init(url: videoURL)
            let videoTimeRange = CMTimeRange.init(start: .zero, duration: videoAsset.duration)
            let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
            if compositionVideoTrack == nil {
                completion(false)
                return
            }
            try compositionVideoTrack!.insertTimeRange(videoTimeRange, of: videoAsset.tracks(withMediaType: .video).first!, at: nextClipStartTime)
            
            let start = CMTime.init(seconds: startTime, preferredTimescale: videoAsset.duration.timescale)
            let duration = CMTime.init(seconds: endTime - startTime, preferredTimescale: videoAsset.duration.timescale)
            let audioTimeRange = CMTimeRange.init(start: start, duration: duration)
            
            //创建最终混合的音频实例
            let audioMix = AVMutableAudioMix()
            
            //添加新的音频
            let audioAsset = AVURLAsset.init(url: audioURL)
            let newAudioTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
            if compositionVideoTrack == nil {
                completion(false)
                return
            }
            try newAudioTrack!.insertTimeRange(audioTimeRange, of: audioAsset.tracks(withMediaType: .audio).first!, at: start)
            let newAudioInputParams = AVMutableAudioMixInputParameters.init(track: newAudioTrack!)
            newAudioInputParams.setVolumeRamp(fromStartVolume: newVolume, toEndVolume: 0.0, timeRange: CMTimeRange.init(start: .zero, duration: videoAsset.duration))
            newAudioInputParams.trackID = newAudioTrack!.trackID
            
            //视频文件原始音频通道
            if isOriginal {
                //视频声音采集(也可不执行这段代码不采集视频音轨，合并后的视频文件将没有视频)
                if videoAsset.tracks(withMediaType: .audio).first != nil {
                    if let originVoiceTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid) {
                        try originVoiceTrack.insertTimeRange(videoTimeRange, of:videoAsset.tracks(withMediaType: .audio).first!, at: .zero)
                        let originAudioInputParams = AVMutableAudioMixInputParameters.init(track: originVoiceTrack)
                        originAudioInputParams.setVolumeRamp(fromStartVolume: newVolume, toEndVolume: 0.0, timeRange: CMTimeRange.init(start: .zero, duration: videoAsset.duration))
                        originAudioInputParams.trackID = originVoiceTrack.trackID
                        audioMix.inputParameters = [newAudioInputParams,originAudioInputParams]
                    } else {
                        audioMix.inputParameters = [newAudioInputParams]
                    }
                } else {
                    audioMix.inputParameters = [newAudioInputParams]
                }
            } else {
                audioMix.inputParameters = [newAudioInputParams]
            }
            
            //创建一个输出
            let assetExport = AVAssetExportSession.init(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
            if assetExport == nil {
                completion(false)
                return
            }
            assetExport!.outputFileType = .mp4
            assetExport!.outputURL = outputFileURL
            assetExport!.shouldOptimizeForNetworkUse = true
            assetExport!.audioMix = audioMix
            
            assetExport!.exportAsynchronously {
                switch assetExport!.status {
                case .unknown:
                    break
                case .waiting:
                    break
                case .exporting:
                    break
                case .completed:
                    completion(true)
                    break
                case .failed:
                    //合成失败
                    completion(false)
                    break
                case .cancelled:
                    completion(false)
                    break
                @unknown default:
                    break
                }
            }
        } catch {
            completion(false)
        }
    }