删除视频背景音乐、添加视频背景音乐

删除视频背景音乐

删除视频的背景音乐其实很简单，把视频数据导入进来，然后我们的视频数据其实是有两条轨道一条是音频，另外一条是视频。由于数据的tracks（轨道包含多条音视频）
是只读的，所以在这里重新创建一个混合器，然后把数据源的视频轨道拿过来。重新生成一个媒体文件，丢弃了音频，这样就将视频的音频给删除掉了。

/** 删除视频的音频 */
    static func remove_video_audio(_ url: URL, finish:@escaping(URL?)->Void) {
        /* 导出的视频路径 */
        let exportURL = URL(fileURLWithPath: get_audio_name("."+url.pathExtension))
        /** 删除重复的文件 */
        try? FileManager.default.removeItem(at: exportURL)
        /* 获取视频数据源 */
        let videoAsset = AVURLAsset(url: url)
        
        // 创建媒体组合器
        let mixComposition = AVMutableComposition()
        /** 时长 */
        let timeRange = CMTimeRangeMake(start: CMTime.zero, duration: videoAsset.duration)
        /** 视频轨道 */
        guard let videoTrack = videoAsset.tracks(withMediaType: .video).last else {
            finish(nil)
            return
        }
        
        /** 混合器 */
        let videoCompositionTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
        try? videoCompositionTrack?.insertTimeRange(timeRange, of: videoTrack, at: CMTime.zero)
        
        //合成输出
        let assetExport = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
        assetExport?.outputURL = exportURL
        /** 设置视频导出格式 */
        var fileType: AVFileType = .mov
        if url.pathExtension == "mp4" {
            fileType = .mp4
        }
        assetExport?.outputFileType = fileType
        assetExport?.shouldOptimizeForNetworkUse = true
        assetExport?.exportAsynchronously(completionHandler: {
            if assetExport?.status == AVAssetExportSession.Status.completed {
                finish(exportURL)
            } else {
                finish(nil)
                print("error = \(assetExport?.error?.localizedDescription ?? "删除视频的音频失败")")
            }
        })
    }

添加视频背景音乐

给视频添加背景音乐，创建一个混合器把传进来的音频和视频添加进去，再按照格式导出。由于是新创建的所以原有的音频会被丢弃。

/** 给视频添加背景音乐 */
    static func video_add_backgroundAudio(_ url: URL, audioURL: URL, finish:@escaping (URL?)->Void) {
        /** 导出视频路径 */
        let exportURL = URL(fileURLWithPath: get_audio_name("."+url.pathExtension))
        /** 删除文件 */
        try? FileManager.default.removeItem(at: exportURL)
        /** 获取数据源 */
        let videoAsset = AVURLAsset(url: url)
        let audioAsset = AVURLAsset(url: audioURL)
        /** 时长 */
        let timeRange = CMTimeRangeMake(start: CMTime.zero, duration: videoAsset.duration)
        /** 音频视频轨道 */
        guard let videoTrack = videoAsset.tracks(withMediaType: .video).last else {
            finish(nil)
            return
        }
        guard let audioTrack = audioAsset.tracks(withMediaType: .audio).last else {
            finish(nil)
            return
        }
        /** 混合器 */
        let mixComposition = AVMutableComposition()
        /** 添加视频轨道 */
        let videoCompositionTrack = mixComposition.addMutableTrack(withMediaType: .video, preferredTrackID: kCMPersistentTrackID_Invalid)
        try? videoCompositionTrack?.insertTimeRange(timeRange, of: videoTrack, at: CMTime.zero)
        /** 添加音频轨道 */
        let audioCompositionTrack = mixComposition.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid)
        try? audioCompositionTrack?.insertTimeRange(timeRange, of: audioTrack, at: CMTime.zero)
        
        /** 合成输出 */
        let assetExport = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
        assetExport?.outputURL = exportURL
        /** 设置视频导出格式 */
        var fileType: AVFileType = .mov
        if url.pathExtension == "mp4" {
            fileType = .mp4
        }
        assetExport?.outputFileType = fileType
        assetExport?.shouldOptimizeForNetworkUse = true
        assetExport?.exportAsynchronously(completionHandler: {
            if assetExport?.status == AVAssetExportSession.Status.completed {
                finish(exportURL)
            } else {
                finish(nil)
                print("error = \(assetExport?.error?.localizedDescription ?? "删除视频的音频失败")")
            }
        })
    }