AVAssetExportSession Error -11820

I'm writing an application that works with video using AVFoundation.

The behaviour of my application is simple: I take a video from the camera roll, then I create an AVMutableComposition with some audio tracks. With the mix compositi开发者_如何学Pythonon i initialize an AVAssetExportSession that stores the video file in the documents directory of my app.

Until this point everything it's ok: my video is stored and I'm able to play it in another controller. If I take the video that i have just stored in my documents folder to make some editing (in the same way of the first time AVmutableComposition, AVAssetExportSession) it's ok again.

But the third time I do this process to editing a video the AVAssetExportSession status becomes "Fail" and with this error:

"Domain=AVFoundationErrorDomain Code=-11820 "Cannot Complete Export" UserInfo=0x1a9260 {NSLocalizedRecoverySuggestion=Try exporting again., NSLocalizedDescription=Cannot Complete Export}"

I have read that is a general error where the session couldn't be exported. What is the sense of this? Why only the third time that i made the editing process? Could it be a memory management mistake? A bug?. This is the code of my AVAssetExportSession:

 _assetExport = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];   
_assetExport.shouldOptimizeForNetworkUse = YES;

///data odierna
NSDateFormatter *format = [[NSDateFormatter alloc] init];
[format setDateFormat:@"ddMMyyyyHHmmss"];

NSDate *now = [[NSDate alloc] init];

NSString *dateString = [format stringFromDate:now];
[now release];
[format release];
NSString* ext = @".MOV";
NSString* videoName=[NSString stringWithFormat:@"%@%@", dateString, ext];

///data odierna
NSString *exportPath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:videoName];

if ([[NSFileManager defaultManager] fileExistsAtPath:exportPath]) 
{
    [[NSFileManager defaultManager] removeItemAtPath:exportPath error:nil];
}


_assetExport.outputFileType = AVFileTypeQuickTimeMovie;

[_assetExport setTimeRange:CMTimeRangeMake(kCMTimeZero, videoAsset.duration)];
NSURL    *exportUrl = [NSURL fileURLWithPath:exportPath] ;

_assetExport.outputURL = exportUrl ;

[_assetExport exportAsynchronouslyWithCompletionHandler:^
{
    switch (_assetExport.status) 
    {
        case AVAssetExportSessionStatusFailed:
        {
            NSLog (@"FAIL %@",_assetExport.error);
            if ([[NSFileManager defaultManager] fileExistsAtPath:[_assetExport.outputURL path]]) 
            {
                [[NSFileManager defaultManager] removeItemAtPath:[_assetExport.outputURL path] error:nil];
            }

            [self performSelectorOnMainThread:@selector (ritenta)
                                   withObject:nil
                                waitUntilDone:NO];
            break;
        }
        case AVAssetExportSessionStatusCompleted: 
        {
            NSLog (@"SUCCESS");

            [self performSelectorOnMainThread:@selector (saveVideoToAlbum:)
                                   withObject:exportPath
                                waitUntilDone:NO];
            break;
        }
        case AVAssetExportSessionStatusCancelled: 
        {
            NSLog (@"CANCELED");

            break;
        }
    };
}];

I have done many searches on the web, some people have had a problem in the outputURL of the session, but I have tried and seems all ok in my code. To assign a unique name to the file I use a NSDate. For debugging purposes I have tried to restore a standard string name but the problem remains. Any ideas? Can someone suggest to me an alternative method to export to the documents folder an asset with AssetWriter insted the AVassetExportSession?

The problem is _assetExport.outputFileType you have set the type AVFileTypeQuickTimeMovie. Which is not likely to be supported type.

Try to find out what output file types are supported by the _assetExport using the following code and use the suitable one.

NSLog (@"created exporter. supportedFileTypes: %@", exporter.supportedFileTypes);

OR
just change the

_assetExport.outputFileType = AVFileTypeQuickTimeMovie;

TO

exporter.outputFileType = @"com.apple.m4a-audio";

Also dont forget to change the extension from

NSString* ext = @".MOV";  to @".m4a" 

This should work. It worked for me.