迅捷：如何删除部分音频？

Question

我正在创建一个简单的音频编辑工具来修剪和删除音频。我实现了修剪功能，并且工作正常。但是我搜索并尝试实现删除功能，这是我的代码：

func deleteExportAsset(_ asset: AVAsset, fileName: String, completeAudioTime: CGFloat) -> URL {
    print("\(#function)")

    let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
    let trimmedSoundFileURL = documentsDirectory.appendingPathComponent(fileName)
    print("saving to \(trimmedSoundFileURL.absoluteString)")

    if FileManager.default.fileExists(atPath: trimmedSoundFileURL.absoluteString) {
        print("sound exists, removing \(trimmedSoundFileURL.absoluteString)")
        do {
            if try trimmedSoundFileURL.checkResourceIsReachable() {
                print("is reachable")
            }

            try FileManager.default.removeItem(atPath: trimmedSoundFileURL.absoluteString)
        } catch {
            print("could not remove \(trimmedSoundFileURL)")
            print(error.localizedDescription)
        }

    }

    print("creating export session for \(asset)")

    if let exporter = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetAppleM4A) {
        exporter.outputFileType = AVFileType.m4a
        exporter.outputURL = trimmedSoundFileURL

        let timeRange1 = CMTimeRangeFromTimeToTime(CMTime(seconds: 0, preferredTimescale: 100), CMTime(seconds: endTimeOfRange1, preferredTimescale: 100))
        let timeRange2 = CMTimeRangeFromTimeToTime(CMTime(seconds: startTimeOfRange2)), preferredTimescale: 100), CMTime(seconds: Double(completeAudioTime), preferredTimescale: 100))
        exporter.timeRange = CMTimeRangeGetUnion(timeRange1, timeRange2)

        // do it
        exporter.exportAsynchronously(completionHandler: {
            print("export complete \(exporter.status)")

            switch exporter.status {
            case  AVAssetExportSessionStatus.failed:

                if let e = exporter.error {
                    print("export failed \(e)")
                }


            case AVAssetExportSessionStatus.cancelled:
                print("export cancelled \(String(describing: exporter.error))")
            default:
                print("export complete")
            }
        })
    } else {
        print("cannot create AVAssetExportSession for asset \(asset)")
    }

    return trimmedSoundFileURL
}

我在这里正在创建2个范围。从0-> time1的Range1和从time2-> endOfAudio的Range2。（我想从时间1->时间2中删除）

然后我在2个范围之间创建并集。但是，音频没有任何反应。它的保存与该功能之前的保存完全相同。

Answer 1

CMTimeRangeGetUnion返回another
CMTimeRange，它只是一个（开始）时间和一个持续时间。因此，没有什么可以容纳完成您期望的两个时间范围。扩展而言，AVASsetExportSession没有API需要导出时间范围
列表 。

但是有一种方法可以实现它。这个想法是创建资产的可编辑副本，删除时间范围，然后导出可编辑副本。AVMutableComposition做这个：

// assuming 'asset', 'endTimeOfRange1' and 'startTimeOfRange2' from the question:

// create empty mutable composition
let composition: AVMutableComposition = AVMutableComposition()
// copy all of original asset into the mutable composition, effectively creating an editable copy
try composition.insertTimeRange( CMTimeRangeMake( kCMTimeZero, asset.duration), of: asset, at: kCMTimeZero)

// now edit as required, e.g. delete a time range
let startTime = CMTime(seconds: endTimeOfRange1, preferredTimescale: 100)
let endTime = CMTime(seconds: startTimeOfRange2, preferredTimescale: 100)
composition.removeTimeRange( CMTimeRangeFromTimeToTime( startTime, endTime))

// since AVMutableComposition is an AVAsset subclass, it can be exported with AVAssetExportSession (or played with an AVPlayer(Item))
if let exporter = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A) 
{
    // configure session and exportAsynchronously as above. 
    // You don't have to set the timeRange of the exportSession
}

请注意，从资产复制到合成仅会修改某些内存结构，这些结构定义了哪些样本在时间轴上到达何处，但实际上并没有移动任何媒体样本。直到导出才完成。结果，编辑（相对）很快，并且您必须至少保留源文件，直到导出完成。