swift - 通过 AVAssetExportSession 导出 mp4 失败

Question

我开始说我花了很多时间搜索文档、此处和其他地方的帖子，但我无法找到解决此问题的方法。

我正在使用 AVAssetExportSession 导出存储在 AVAsset 实例中的 .mp4 文件。我所做的是:

• 我检查 AVAsset 的 isExportable 属性
• 然后我得到一个与 AVAsset 实例兼容的 exportPresets 数组
• 我采用 AVAssetExportPreset1920x1080，或者，如果不存在，我尝试使用 AVAssetExportPresetPassthrough 导出媒体(仅供引用，100% 的时候，我需要的预设总是包含在列表中，但我也尝试了 passthrough 选项，但无论如何它都不起作用)

outputFileType 是 AVFileTypeMPEG4 我也尝试过为文件分配 .mp4 扩展名，但没有任何效果。我总是收到这个错误

Error Domain=AVFoundationErrorDomain Code=-11838 "Operation Stopped" UserInfo={NSUnderlyingError=0x600000658c30 {Error Domain=NSOSStatusErrorDomain Code=-12109 "(null)"}, NSLocalizedFailureReason=The operation is not supported for this media., NSLocalizedDescription=Operation Stopped}

下面是我使用的代码

func _getDataFor(_ item: AVPlayerItem, completion: @escaping (Data?) -> ()) {
    guard item.asset.isExportable else {
        completion(nil)
        return
    }

    let compatiblePresets = AVAssetExportSession.exportPresets(compatibleWith: item.asset)
    var preset: String = AVAssetExportPresetPassthrough
    if compatiblePresets.contains(AVAssetExportPreset1920x1080) { preset = AVAssetExportPreset1920x1080 }

    guard
        let exportSession = AVAssetExportSession(asset: item.asset, presetName: preset),
        exportSession.supportedFileTypes.contains(AVFileTypeMPEG4) else {
        completion(nil)
        return
    }

    var tempFileUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0].appendingPathComponent("temp_video_data.mp4", isDirectory: false)
    tempFileUrl = URL(fileURLWithPath: tempFileUrl.path)

    exportSession.outputURL = tempFileUrl
    exportSession.outputFileType = AVFileTypeMPEG4
    let startTime = CMTimeMake(0, 1)
    let timeRange = CMTimeRangeMake(startTime, item.duration)
    exportSession.timeRange = timeRange

    exportSession.exportAsynchronously {
        print("\(exportSession.error)")
        let data = try? Data(contentsOf: tempFileUrl)
        _ = try? FileManager.default.removeItem(at: tempFileUrl)
        completion(data)
    }
}

Answer 1

似乎在 AVMutableComposition 中转换 AVAsset 实例就成功了。如果有人知道此方法有效的原因，请告诉我。

这是新的_getDataFor(_:completion:)方法实现

func _getDataFor(_ item: AVPlayerItem, completion: @escaping (Data?) -> ()) {
    guard item.asset.isExportable else {
        completion(nil)
        return
    }

    let composition = AVMutableComposition()
    let compositionVideoTrack = composition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))
    let compositionAudioTrack = composition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))

    let sourceVideoTrack = item.asset.tracks(withMediaType: AVMediaTypeVideo).first!
    let sourceAudioTrack = item.asset.tracks(withMediaType: AVMediaTypeAudio).first!
    do {
        try compositionVideoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, item.duration), of: sourceVideoTrack, at: kCMTimeZero)
        try compositionAudioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, item.duration), of: sourceAudioTrack, at: kCMTimeZero)
    } catch(_) {
        completion(nil)
        return
    }

    let compatiblePresets = AVAssetExportSession.exportPresets(compatibleWith: composition)
    var preset: String = AVAssetExportPresetPassthrough
    if compatiblePresets.contains(AVAssetExportPreset1920x1080) { preset = AVAssetExportPreset1920x1080 }

    guard
        let exportSession = AVAssetExportSession(asset: composition, presetName: preset),
        exportSession.supportedFileTypes.contains(AVFileTypeMPEG4) else {
        completion(nil)
        return
    }

    var tempFileUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0].appendingPathComponent("temp_video_data.mp4", isDirectory: false)
    tempFileUrl = URL(fileURLWithPath: tempFileUrl.path)

    exportSession.outputURL = tempFileUrl
    exportSession.outputFileType = AVFileTypeMPEG4
    let startTime = CMTimeMake(0, 1)
    let timeRange = CMTimeRangeMake(startTime, item.duration)
    exportSession.timeRange = timeRange

    exportSession.exportAsynchronously {
        print("\(tempFileUrl)")
        print("\(exportSession.error)")
        let data = try? Data(contentsOf: tempFileUrl)
        _ = try? FileManager.default.removeItem(at: tempFileUrl)
        completion(data)
    }
}