如何導出視頻的任意片段？ 導出視頻的最后X秒時出現“操作停止”錯誤

Question

目標是導出某些視頻的任意片段（例如，中間三分之一，最后一半），但是AVAssetExportSession僅在起點是視頻的起點時成功。

如果cmStartTime不為0，則AVAssetExportSession失敗，並顯示以下錯誤：

失敗：可選（錯誤域= AVFoundationErrorDomain代碼= -11841“操作已停止” UserInfo = 0x175872d00 {NSLocalizedDescription =操作已停止，NSLocalizedFailureReason =無法合成視頻。}）。

    // Create main composition & its tracks
    let mainComposition = AVMutableComposition()
    let compositionVideoTrack = mainComposition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))
    let compositionAudioTrack = mainComposition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))

    // Get source video & audio tracks
    let videoURL = NSURL(fileURLWithPath: fileURL)
    let videoAsset = AVURLAsset(URL: videoURL, options: nil)
    let sourceVideoTrack = videoAsset.tracksWithMediaType(AVMediaTypeVideo)[0]
    let sourceAudioTrack = videoAsset.tracksWithMediaType(AVMediaTypeAudio)[0]

    // Define time values for video
    let timescale = Int32(600)
    let cmStartTime = CMTimeMake(Int64(CGFloat(0.5) * CGFloat(timescale)), timescale)
    let cmEndTime = CMTimeMake(10, 1)
    let timeRange = CMTimeRangeMake(cmStartTime, cmEndTime)

    // Add source tracks to composition
    do {
        try compositionVideoTrack.insertTimeRange(timeRange, ofTrack: sourceVideoTrack, atTime: cmStartTime)
        try compositionAudioTrack.insertTimeRange(timeRange, ofTrack: sourceAudioTrack, atTime: cmStartTime)
    } catch {
        printError("Error with insertTimeRange while exporting video: \(error)")
    }

    // Create video composition
    let renderSize = compositionVideoTrack.naturalSize
    let videoComposition = AVMutableVideoComposition()
    videoComposition.renderSize = renderSize
    videoComposition.frameDuration = CMTimeMake(Int64(1), Int32(frameRate))

    // Add layer instruction to video composition
    ...

    // Apply effects to video
    ...

    // Define export URL
    let exportPath = getUniqueTempPath(gMP4File)
    let exportURL = NSURL(fileURLWithPath: exportPath)

    // Create exporter
    let exporter = AVAssetExportSession(asset: mainComposition, presetName: AVAssetExportPresetHighestQuality)!
    exporter.videoComposition = videoComposition
    exporter.outputFileType = AVFileTypeMPEG4
    exporter.outputURL = exportURL
    exporter.shouldOptimizeForNetworkUse = true
    exporters.append(exporter)

    // Export video
    exporter.exportAsynchronouslyWithCompletionHandler() {
        // Finish stuff
    }

Answer 1

問題來自於不了解CMTimeRangeMake和insertTimeRange 。

CMTimeRangeMake的第二個值應該是剪輯的持續時間，而不是結束時間。 因此，如果您的開始時間是5秒標記，並且剪輯持續10秒，則第二個值應該是10，而不是15。

該atTime的參數insertTimeRange應kCMTimeZero ，因為我們的目標是創建一個新的剪輯。 換句話說，此值表示要在新軌道中從源軌道插入剪輯的位置。