12780 ошибка quicktime

I have a problem tracing the underlying issue behind my asset export session failure. The issue is for one video only, and I believe the problem is in its audio track, since I successfully exported the asset without the audio track (only the video track).

The video track is decoded with AVAssetReader and the sample buffers are processed before being rewritten into a new video track; the audio track is passed with no decoding nor any intermediate processing. However, even without processing the video sample buffers, the same failure occurred.

I also tried doing it the other way round—with audio only and no video track—and still other videos worked just fine and this particular video failed. I suppose there’s an inherent problem with the video’s audio track, but I can’t infer what the problem is, and hence I can’t tackle it. Here’s my code:

AVAssetExportSession* assetExport = [[AVAssetExportSession alloc] initWithAsset:composition
                                                                      presetName:AVAssetExportPresetHighestQuality];

assetExport.outputFileType = @"com.apple.quicktime-movie";
assetExport.outputURL = [NSURL fileURLWithPath:path];

__weak typeof(self) weakSelf = self;
[assetExport exportAsynchronouslyWithCompletionHandler:^{

    switch (assetExport.status) {
        case AVAssetExportSessionStatusCompleted: NSLog(@"Asset combined");
            break;
        case AVAssetExportSessionStatusFailed: NSLog(@"Asset combination failed");
            break;
        default: NSLog(@"Asset combination completed with unknown status: %@", @(assetExport.status));
            break;
    }
}];

The problem is supposed to be in the asset export session; track insertion to the AVMutableComposition worked just fine. Here’s the error message of the AVAssetExportSession:

Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed"
UserInfo={NSUnderlyingError=0x6040001338d0 {Error Domain=NSOSStatusErrorDomain Code=-12780 "(null)"}, 
NSLocalizedFailureReason=An unknown error occurred (-12780), NSLocalizedDescription=The operation could not be completed}

I’m trying to merge some audio files (picked via MPMediaPickerController), but the export always fails with error code -12780.

When I try to play my composition with an AVPlayer object, it plays correctly.
Just the export fails.

What am I doing wrong?

This is my code:

AVAssetExportSession *exportSession;
AVPlayer *player;

- (void)mergeAudiofiles {
    // self.mediaItems is an NSArray of MPMediaItems
    if (self.mediaItems.count == 0) {
        UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error"
                                                        message:@"No Tracks selected."
                                                       delegate:nil
                                              cancelButtonTitle:@"OK"
                                              otherButtonTitles:nil];
        [alert show];
        return;
    }

    // Configure audio session
    NSError *sessionError;
    AVAudioSession *session = [AVAudioSession sharedInstance];
    [session setCategory:AVAudioSessionCategoryAudioProcessing error:nil];
    [session setActive:YES error:&sessionError];
    if (sessionError) NSLog(@"Session-Error: %@", sessionError.localizedDescription);

    // Create composition
    AVMutableComposition *composition = [AVMutableComposition composition];
    AVMutableCompositionTrack *track = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    CMTime position = kCMTimeZero;

    for (MPMediaItem *item in self.mediaItems) {
        NSURL *assetURL = [item valueForProperty:MPMediaItemPropertyAssetURL];
        AVAsset *asset  = [AVAsset assetWithURL:assetURL];

        CMTimeRange duration = CMTimeRangeMake(kCMTimeZero, asset.duration);
        //        duration = CMTimeRangeMake(kCMTimeZero, CMTimeMake(5, 1));    // For player test

        NSError *error;
        [track insertTimeRange:duration ofTrack:[[asset tracksWithMediaType:AVMediaTypeAudio] lastObject] atTime:position error:&error];
        if (error) NSLog(@"ERROR! :(");

        position = CMTimeAdd(position, duration.duration);
    }

    // Path to output file
    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSURL *exportUrl = [NSURL URLWithString:[documentsDirectory stringByAppendingPathComponent:@"export.m4a"]];

    NSLog(@"Export URL = %@", exportUrl.description);

    //    Playing works!
    //    """"""""""""""
    //    AVPlayerItem *pitem = [[AVPlayerItem alloc] initWithAsset:composition];
    //    player = [[AVPlayer alloc] initWithPlayerItem:pitem];
    //    [player play];
    //
    //    return;

    // Export
    exportSession = [[AVAssetExportSession alloc] initWithAsset:composition presetName:AVAssetExportPresetAppleM4A];
    exportSession.outputURL = exportUrl;
    exportSession.outputFileType = AVFileTypeAppleM4A;

    [exportSession exportAsynchronouslyWithCompletionHandler:^{
        switch (exportSession.status) {
            case AVAssetExportSessionStatusFailed:
                NSLog(@"Export failed -> Reason: %@, User Info: %@",
                      exportSession.error.localizedDescription,
                      exportSession.error.userInfo.description);
                break;

            case AVAssetExportSessionStatusCancelled:
                NSLog(@"Export cancelled");
                break;

            case AVAssetExportSessionStatusCompleted:
                NSLog(@"Export finished");
                break;

            default:
                break;
        }
    }];
}