視頻並不總是導出到相機膠卷：NSFileManager 的 removeItemAtPath 非阻塞？

Question

閱讀幾個教程后，像這樣的，看着其他代碼導出視頻，我們仍然無法解決問題。

有時新視頻會導出到相機膠卷，有時則不會。 我們甚至無法始終如一地重現該問題。

我們可以想象的唯一問題是NSFileManager.defaultManager().removeItemAtPath是否不是阻塞調用，但沒有文檔表明它是異步的，所以我們假設情況並非如此。

每次， writeVideoAtPathToSavedPhotosAlbum閉包中的“已保存視頻” println都會被調用，表明視頻已成功寫入相機膠卷，但我們在那里看不到視頻。

關於如何排除故障的建議？

代碼：

        // -- Get path
        let fileName = "/editedVideo.mp4"
        let allPaths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
        let docsPath = allPaths[0] as! NSString
        let exportPath = docsPath.stringByAppendingFormat(fileName)
        let exportUrl = NSURL.fileURLWithPath(exportPath as String)!

        println(exportPath)

        // -- Remove old video?
        if NSFileManager.defaultManager().fileExistsAtPath(exportPath as String) {
            println("Deleting existing file\n")
            NSFileManager.defaultManager().removeItemAtPath(exportPath as String, error: nil)
        }

        // -- Create exporter
        let exporter = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
        exporter.videoComposition = mutableComposition
        exporter.outputFileType = AVFileTypeMPEG4
        exporter.outputURL = exportUrl
        exporter.shouldOptimizeForNetworkUse = true

        // -- Export video
        exporter.exportAsynchronouslyWithCompletionHandler({
            self.exportDidFinish(exporter)
        })
    }


    func exportDidFinish(exporter: AVAssetExportSession) {
        println("Finished exporting video!")

        // Write out video to photo album
        let assetLibrary = ALAssetsLibrary()
        assetLibrary.writeVideoAtPathToSavedPhotosAlbum(exporter.outputURL, completionBlock: {(url: NSURL!, error: NSError!) in
            println("Saved video \(exporter.outputURL)")

            if (error != nil) {
                println("Error saving video")
            }
        })
    } 

Answer 1

一些可能有助於解決您的問題的建議：

1. 檢查為已完成的視頻有效/與磁帶庫兼容這里

   if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:videoURL]) { [library writeVideoAtPathToSavedPhotosAlbum:videoURL completionBlock:^(NSURL *assetURL, NSError *error){} ]; }

2. 確保傳回的資產 url 不是此處引用的 nil

    if(error){ NSLog(@"Error: Domain = %@, Code = %@", [error domain], [error localizedDescription]); } else if(assetURL == nil){ //It's possible for writing to camera roll to fail, without receiving an error message, but assetURL will be nil //Happens when disk is (almost) full NSLog(@"Error saving to camera roll: no error message, but no url returned"); } else { //remove temp file NSError *error; [[NSFileManager defaultManager] removeItemAtURL:fileURL error:&error]; if(error){ NSLog(@"error: %@", [error localizedDescription]); } }

3. 考慮使用 PHPhotoLibrary 來導出視頻

   PHPhotoLibrary.sharedPhotoLibrary().performChanges({ let assetRequest = PHAssetChangeRequest.creationRequestForAssetFromVideoAtFileURL(videoURL) let assetPlaceholder = assetRequest.placeholderForCreatedAsset }, completionHandler: { success, error in // check and handle error // do something with your asset local identifier })