Audio export fail iOS Swift - ios

Question

I'm trying to concatenate two audio files with the following code:
func concatenateFiles(audioFiles: [NSURL], completion: (concatenatedFile: NSURL?) -> ()) {
// Result file
var nextClipStartTime = kCMTimeZero
let composition = AVMutableComposition()
let track = composition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: kCMPersistentTrackID_Invalid)
// Add each track
for audio in audioFiles {
let asset = AVURLAsset(URL: NSURL(fileURLWithPath: audio.path!), options: nil)
if let assetTrack = asset.tracksWithMediaType(AVMediaTypeAudio).first {
let timeRange = CMTimeRange(start: kCMTimeZero, duration: asset.duration)
do {
try track.insertTimeRange(timeRange, ofTrack: assetTrack, atTime: nextClipStartTime)
nextClipStartTime = CMTimeAdd(nextClipStartTime, timeRange.duration)
} catch {
print("Error concatenating file - \(error)")
completion(concatenatedFile: nil)
return
}
}
}
// Export the new file
if let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetPassthrough) {
let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
let documents = NSURL(string: paths.first!)
if let fileURL = documents?.URLByAppendingPathComponent("\(stringFromDate(NSDate())).m4a") {
// Remove existing file
do {
try NSFileManager.defaultManager().removeItemAtPath(fileURL.path!)
print("Removed \(fileURL)")
} catch {
print("Could not remove file - \(error)")
}
// Configure export session output
exportSession.outputURL = fileURL
exportSession.outputFileType = AVFileTypeAppleM4A
// Perform the export
exportSession.exportAsynchronouslyWithCompletionHandler() { handler -> Void in
if exportSession.status == .Completed {
print("Export complete")
dispatch_async(dispatch_get_main_queue(), {
completion(concatenatedFile: fileURL)
})
return
} else if exportSession.status == .Failed {
print("Export failed - \(exportSession.error)")
}
completion(concatenatedFile: nil)
return
}
}
}
}
but i've receive this error exporting the file:
Export failed - Optional(Error Domain=AVFoundationErrorDomain Code=-11838 "Operation Stopped" UserInfo={NSLocalizedDescription=Operation Stopped, NSLocalizedFailureReason=The operation is not supported for this media.})
i've try to change the format but doesnt work, i have no more idea,
there's some one can help me?

Answer 1

I really don't know why, but the problem was solved when i change the attribution of the outputURL in the exportSession,
before:
exportSession.outputURL = fileURL
now:
exportSession.outputURL = NSURL.fileURLWithPath(fileURL.path!)