Your method exportAudio:toFilePath:
is actually an asynchronous method and requires a few fixes to become a proper asynchronous method.
First, you should provide a completion handler in order to signal the call-site that the underlying task has been finished:
- (void)exportAudio:(AVAsset *)avAsset
toFilePath:(NSString *)filePath
completion:(completion_t)completionHandler;
Note, that the result of the method is passed through the completion handler, whose signature might be as follows:
typedef void (^completion_t)(id result);
where parameter result is the eventual result of the method. You should always return an NSError
object when anything goes wrong when setting up the various objects within the method - even though, the method could return an immediate result indicating an error.
Next, if you take a look into to documentation you can read:
requestMediaDataWhenReadyOnQueue:usingBlock:
- (void)requestMediaDataWhenReadyOnQueue:(dispatch_queue_t)queue
usingBlock:(void (^)(void))block
Discussion
The block should append media data to the input either until the input’s readyForMoreMediaData property becomes NO or until there is no more media data to supply (at which point it may choose to mark the input as finished using markAsFinished). The block should then exit. After the block exits, if the input has not been marked as finished, once the input has processed the media data it has received and becomes ready for more media data again, it will invoke the block again in order to obtain more.
You should now be quite sure when your task is actually finished. You determine this within the block which is passed to the method requestMediaDataWhenReadyOnQueue:usingBlock:
.
When the task is finished you call the completion handler completionHandler provided in
method exportAudio:toFilePath:completion:
.
Of course, you need to fix your implementation, e.g. having the method ending with
tracks = nil;
writer = nil;
writerInput = nil;
reader = nil;
readerOutput=nil;
mediaInputQueue = nil;
return returnValue;
//return YES;
}
makes certainly no sense. Cleaning up and returning a result shall be done when the asynchronous task is actually finished. Unless an error occurs during setup, you need to determine this in the block passed to the method requestMediaDataWhenReadyOnQueue:usingBlock:
.
In any case, in order to signal the result to the call-site call the completion handler completionHandler and pass a result object, e.g. if it succeeded the URL where it has been saved, otherwise an NSError
object.
Now, since our method startUploadSongAnalysis
is calling an asynchronous method, this method inevitable becomes asynchronous as well!
If I understood your original code correctly, you are invoking it recursively in order to process a number of assets. In order to implement this correctly, you need a few fixes shown below. The resulting "construct" is NOT a recursive method though, but instead an iteratively invocation of an asynchronous method ("asynchronous loop").
You may or may not provide a completion handler - same as above. It's up to you - but I would recommend it, it won't hurt to know when all assets have been processed. It may look as follows:
-(void)startUploadSongAnalysisWithCompletion:(completion_t)completionHandler
{
[self updateProgressYForID3NForUpload:NO];
// *** check for break condition: ***
if ([self.uploadWorkingAray count]>=1)
{
... stuff
//export low bitrate song to cache
[self exportAudio:[AVAsset assetWithURL:songU]
toFilePath:savedPath
completion:^(id urlOrError)
{
if ([urlOrError isKindOfClass[NSError class]]) {
// Error occurred:
NSLog(@"Error: %@", urlOrError);
// There are two alternatives to proceed:
// A) Ignore or remember the error and proceed with the next asset.
// In this case, it would be best to have a result array
// containing all the results. Then, invoke
// startUploadSongAnalysisWithCompletion: in order to proceed
// with the next asset.
//
// B) Stop with error.
// Don't call startUploadSongAnalysisWithCompletion: but
// instead invoke the completion handler passing it the error.
// A:
// possibly dispatch to a sync queue or the main thread!
[self.uploadWorkingAray removeObjectAtIndex:0];
[self.songNotFoundArray addObject:songVar];
// *** next song: ***
[self startUploadSongAnalysisWithCompletion:completionHandler];
}
else {
// Success:
// *** next song: ***
NSURL* url = urlOrError;
[self startUploadSongAnalysisWithCompletion:completionHandler];
}
}];
}
else //uploadWorkingAray empty
{
NSLog(@"save changes");
[[VPPCoreData sharedInstance] saveAllChanges];
// *** signal completion ***
if (completionHandler) {
completionHandler(@"OK");
}
}
}