I just began learning about AudioQueues from the CoreAudio book (rough cuts).
I did the AudioQueue playback example tutorial, which is basically the same as the apple tutorial example. Everything is working fine.
The problems start when I try to implement the code in an app with a GUI. I tested it by pasting the code into the 'init' method of a NSObject subclass. The only way I can get the queue to do the callback is by inserting an empty DO...WHILE loop in the end of my init, but that makes the GUI freeze (obviously...)!!
Apparently the AudioQueue is supposed to be run in its own separate thread automatically as long as AudioQueueNewOutput is passed NULL for inCallbackRunLoop and CallbackRunLoopMode arguments. That's just not happening. I am only hearing the 1.5 seconds from the priming of the buffers.
Clearly, there is something fundamental that I don't understand about how things work...
Kasper
-(void) start
{
CheckError(
AudioQueueStart(queue, NULL),
"AudioQueueStart failed");
printf("Playing...\n");
do {
} while (0 == 0); //WHY IS THIS MAKING IT PLAY???
}
Turns out that my userData struct wasn't declared as a ivar in the header file. Rookie mistake...
Related
I am doing an application that involves playing back a song in a multi track format (drums, vocals, guitar, piano, etc...). I don't need to do any fancy audio processing to each track, all I need to be able to do is play, pause, and mute/unmute each track.
I had been using multiple instances of AVAudioPlayer but when performing device testing, I noticed that the tracks are playing very slightly out of sync when they are first played. Furthermore, when I pause and play the tracks they continue to get more out of sync. After a bit of research I've realized that AVAudioplayer just has too much latency and won't work for my application.
In my application I basically had an NSArray of AVAudioPlayers that I would loop through and play each one or pause/stop each one, I'm sure this is what caused it to get out of sync on the device.
It seemed like apple's audio mixer would work well for me, but when I try implementing it I get a EXC_BAD_ACCESS error that I can't figure out.
I know the answer is to use OpenAL or audio units but It just seems unnecessary to spend weeks learning about these when all I need to do is play around 5 .mp3 tracks at the same time. Does anyone have any suggestions on how to accomplish this? Thanks
thanks to admsyn's suggestion I was able to come up with a solution.
AVAudioPlayer has a currentTime property that returns the current time of a track and can also be set.
So I implemented the startSynchronizedPlayback as stated by admsyn and then added the following when I stopped the tracks:
-(void) stopAll
{
int count = [tracksArr count];
for(int i = 0; i < count; i++)
{
trackModel = [tracksArr objectAtIndex:i]
if(i = 0)
{
currentTime = [trackModel currentTime]
}
[trackModel stop]
[trackModel setCurrentTime:currentTime]
}
{
This code basically loops through my array of tracks which each hold their own AVAudioPlayer, grabs the current time from the first track, then sets all of the following tracks to that time. Now when I use the startSynchronizedPlayback method they all play in sync, and pausing unpausing keeps them in sync as well. Hope this is helpful to someone else trying to keep tracks in sync.
If you're issuing individual play messages to each AVAudioPlayer, it is entirely likely that the messages are arriving at different times, or that the AVAudioPlayers finish their warm up phase out of sync with each other. You should be using playAtTime: and the deviceCurrentTime property to achieve proper synchronization. Note the description of deviceCurrentTime:
Use this property to indicate “now” when calling the playAtTime: instance method. By configuring multiple audio players to play at a specified offset from deviceCurrentTime, you can perform precise synchronization—as described in the discussion for that method.
Also note the example code in the playAtTime: discussion:
// Before calling this method, instantiate two AVAudioPlayer objects and
// assign each of them a sound.
- (void) startSynchronizedPlayback {
NSTimeInterval shortStartDelay = 0.01; // seconds
NSTimeInterval now = player.deviceCurrentTime;
[player playAtTime: now + shortStartDelay];
[secondPlayer playAtTime: now + shortStartDelay];
// Here, update state and user interface for each player, as appropriate
}
If you are able to decode the files to disk, then audio units are probably the solution which would provide the best latency. If you decide to use such an architecture, you should also check out Novocaine:
https://github.com/alexbw/novocaine
That framework takes a lot of the headache out of dealing with audio units.
I have been working on an opencv project for iOS. I was given a simple project to start developing with that captured and displayed frames. I never payed much attention to how it worked until I started having memory issues and traced them back to the original project setup. I now plan to re-write the capturing/displaying code but I don't understand why it worked in the first place. There was a play/pause button which called the method
- (IBAction)play_pause:(id)sender
{
play = !play;
while(play)
{
if (_videoCapture && _videoCapture->grab())
{
(*_videoCapture) >> _display_frame;
//process frame
self.imageView.image = [UIImage imageWithCVMat:_display_frame];
}
}
}
play is just a global bool that signifies whether the application is playing or paused. The strange thing is that the processing should be taking place inside an infinite loop, there is no way out. play is never modified within the loop. In spite of that, when the application is running the play/pause button remains responsive and is capable of flipping the play bool and pausing the execution. Not only that, other bools (use_greyscale for instance) can be flipped by other buttons and their values change inside the loop. I would have expected the application to freeze and never even draw new frames to the screen. The application should stay trapped inside that function for most of its lifetime, unable to perform other tasks such as drawing and UIControl. It seems as though the only way this is possible is if the IBAction call is running on its own thread. I cannot find any evidence of threading in the source code. Could someone explain how apple handles threading in its UI? I was under the impression that there was one main runloop thread and that extra threads were not created automatically. If that is true, how can this behavior be explained?
side note-
What finally made me investigate this was that [UIImage imageWithCVMat:_display_frame] returns an auto-released object. Since all this takes place inside a loop, the objects could not be released without the execution being paused which was causing crashes.
The reason is worked is because the implementation of the cv::VideoCapture::grab() method runs the current run loop to pause the thread until it gets a frame.
When you launch your application, the main function executes a function named UIApplicationMain, which executes CFRunLoopRun. When CFRunLoopRun is executed on the main thread, it runs the main run loop, which is the run loop that processes all the UI events received from the system and refresh the user interface. For information on run loops, you may read Apple Threading Programming Guide.
So, when you execute an infinite loop, your code never returns to the run loop and the waiting events cannot be processed. But in your case, the grab method runs the run loop again with an expiration delay. So the run loop may process incoming events (which may invoke your code again) until the delay expires, then return to your code that will run the run loop again.
If you look at the callstack when you touch the button to pause, you will see this:
main function → run loop → event handling → your code → OpenCV → run loop → event handling → your code
The run loop is running inside itself, which is perfectly fine because run loops are reentrant. Scroll views actually use that behavior: When you scroll a UIScrollView, it runs the run loop again in a different mode in order to ignore some events until you end scrolling.
But I'm not sure the developers of OpenCV had this in mind when they wrote their code. So I think it would be better to load your frames in a background thread/queue.
You are correct, there is no "automatic threading" in iOS. Grand Central Dispatch (GCD) certainly makes threading much easier, but it does not happen automatically.
You can write some debug code and test for [NSThread isMainThread] in the while loop to see if play_pause is indeed being run on the main UI thread, which I suspect it is not.
for my game iOS project I need a ring buffer. It should work similar to a queue where elements go out and go in but the total amount of elements in the buffer should stay the same.
I implemented the ring buffer successfully using java but I am not so familar with objective-c. I found a ring buffer implementation on the web called CHCircularBuffer: https://bitbucket.org/devartum/chdatastructures/src/4d6d7194ee94/source/CHCircularBuffer.m However I failed implementing it correctly.
The circular buffer is a property of a class called TerrainManager which does all the mathematical terrain generation.
#interface TerrainManager : NSObject{
int terrainParts;
CHCircularBuffer* circularTerrainBuffer;
}
#property(nonatomic, retain) CHCircularBuffer *circularTerrainBuffer;
#end
This how the ring buffer is initialized in the implementation of TerrainManager
circularTerrainBuffer = [[CHCircularBuffer alloc] initWithCapacity:parts];
This creates an instance of the buffer and sets the size property to parts. Now I add objects to the buffer using addObject method:
[circularTerrainBuffer addObject:[NSNumber numberWithDouble:0.2]];
Sometimes this line receives an error "exec_bad_access". E.g. when I init the buffer with capacity of 15 everything is fine, with 20 I get the error.
I now try to access the buffer from the terrain class where the drawing takes place. But whenever I try to access the objects I get an "bad_access" error.
NSArray *arr = [terrainManager.circularTerrainBuffer allObjects];
E.g. this line would create the error.
So there is something wrong with my code. Maybe I dont understand the buffer and add objects the wrong way. I dont know. Any ideas or suggestions?
The snippets of code you are showing are correct. I implemented a small project to test CHCircularBuffer the way you specify and it works correctly. So, the problem must be somewhere else.
The only way around this is, IMHO, put a breakpoint on the line that fails and step into the addObject function to see where exactly it fails. The array could be reallocated in there, so may be this is failing and giving the bad access. The same for allObjects.
Anyway, I have to say that I could execute my test without any issue, adding objects, removing them from head and tail, and getting the array of all objects with no issues.
If you post more code, we can maybe help a bit more.
following is .m code:
#import "ThreadLabAppDelegate.h"
#interface ThreadLabAppDelegate()
- (void)processStart;
- (void)processCompleted;
#end
#implementation ThreadLabAppDelegate
#synthesize isProcessStarted;
- (void)awakeFromNib {
//Set levelindicator's maximum value
[levelIndicator setMaxValue:1000];
}
- (void)dealloc {
//Never called while debugging ????
[super dealloc];
}
- (IBAction)startProcess:(id)sender {
//Set process flag to true
self.isProcessStarted=YES;
//Start Animation
[spinIndicator startAnimation:nil];
//perform selector in background thread
[self performSelectorInBackground:#selector(processStart) withObject:nil];
}
- (IBAction)stopProcess:(id)sender {
//Stop Animation
[spinIndicator stopAnimation:nil];
//set process flag to false
self.isProcessStarted=NO;
}
- (void)processStart {
int counter = 0;
while (counter != 1000) {
NSLog(#"Counter : %d",counter);
//Sleep background thread to reduce CPU usage
[NSThread sleepForTimeInterval:0.01];
//set the level indicator value to showing progress
[levelIndicator setIntValue:counter];
//increment counter
counter++;
}
//Notify main thread for process completed
[self performSelectorOnMainThread:#selector(processCompleted) withObject:nil waitUntilDone:NO];
}
- (void)processCompleted {
//Stop Animation
[spinIndicator stopAnimation:nil];
//set process flag to false
self.isProcessStarted=NO;
}
#end
I need to clear following things as per the above code.
How to interrupt/cancel processStart while loop from UI control?
I also need to show the counter value in main UI, which i suppose to do with performSelectorOnMainThread and passing argument. Just want to know, is there anyother way to do that?
When my app started it is showing 1 thread in Activity Monitor, but when i started the processStart() in background thread its creating two new thread,which makes the total 3 thread until or unless loop get finished.After completing the loop i can see 2 threads.
So, my understanding is that, 2 thread created when i called performSelectorInBackground, but what about the thrid thread, from where it got created?
What if thread counts get increases on every call of selector.How to control that or my implementation is bad for such kind of requirements?
Thanks
how to update UI controls in cocoa application from background thread
Simple: Don't.
How to interrupt/cancel processStart while loop from UI control?
Outside of processStart, set a flag variable. Inside of processStart, check that flag and exit the loop if it is set.
Don't try to “kill” a thread from another thread. It's always a bad idea. Tell the thread it's time to stop by setting the flag, and have the thread check that flag and stop at an appropriate time.
I also need to show the counter value in main UI, which i suppose to do with performSelectorOnMainThread and passing argument. Just want to know, is there anyother way to do that?
Yes.
When my app started it is showing 1 thread in Activity Monitor, but when i started the processStart() in background thread its creating two new thread,which makes the total 3 thread until or unless loop get finished.After completing the loop i can see 2 threads. So, my understanding is that, 2 thread created when i called performSelectorInBackground, but what about the thrid thread, from where it got created?
Profile your app using Instruments or Shark and look. It's probably the heartbeat thread for the progress indicator.
What if thread counts get increases on every call of selector.How to control that or my implementation is bad for such kind of requirements?
Every performSelectorInBackground:withObject: message starts a thread. If your thread count isn't going down, it's because your thread method didn't exit. If your thread count is too high, it's (probably) because you started too many threads.
There is a much better way to do this.
First, the general rule in Cocoa is never sleep. Think of this as special ultra-caffeinated Cocoa. For anything you might sleep for in another framework, there is almost always a better, usually easier, way in Cocoa.
With that in mind, look at processStart. All it does is do something every centisecond. How best to do that?
Cocoa has a class for this specific purpose: NSTimer. Create a timer that sends yourself a message at the desired interval, and respond to that message by updating the progress bar—that is, your timer callback method should essentially just be the loop body from processStart, without the loop.
By the way, 100 updates per second is overkill. First off, the user does not care that you have made 1/5th of a pixel's worth of progress since the last time you updated the bar. Second, the screen only updates about 60 times per second anyway, so updating anything visible faster than that is pointless.
- (void)dealloc {
//Never called while debugging ????
[super dealloc];
}
Assuming you put your app delegate in the MainMenu nib, the application object owns it because of that—but it doesn't know that, because it only knows about the app delegate as its delegate, which is a non-owning relationship. (And even if it were an owning relationship, that would just be two ownerships, of which the app would release one, which wouldn't help.)
However, the lifetime of the app delegate doesn't really matter. Its purpose as the delegate of the application means that it needs to last about as long as the application does, but when the application goes away, the process is exiting, which means the delegate will be deallocated as well, as part of the reclamation of the process's memory space. That's why dealloc isn't called—the whole process space goes away at once, instead of objects being deallocated one at a time.
So, in principle, yeah, the app delegate not getting explicitly cleaned up is kind of dodgy. In practice, don't put any temporary-files clean-up in its dealloc (use applicationWillTerminate: instead) and you'll be fine.
I typically work around the problem by putting all my real work in one or more other objects which the app delegate owns. The app delegate creates these other controllers in applicationWillFinishLaunching: and releases them in applicationWillTerminate:, so those objects do get dealloc messages. Problem solved.
I'm working on a simple proof-of-concept for an iPhone app (and important bit of info, I'm pretty new to Mac OSX development all around). I created a view based app with a timer. I declared my NSTimer in the interface of my app's controller, used #property and #synthesize, and I initialize it in the controller's viewDidLoad method with scheduledTimerWithTimeInterval method. My selector is a method with the signature -(void)someMethod:(NSTimer *)timer which is declared in the interface and defined in the implementation file of the controller as well. I can step past the line where I assign the timer and see that it points to a valid object, but my program goes no further than the end of the viewDidLoad method and never reaches the breakpoint at the first line of my method that is called by the timer. Also, I see GDB: Program received bad signal: "EXC_BAD_ACCESS" in the status bar of xcode at this point (viewDidLoad end is reached). I didn't do anything in IB but add a view and a picker just so I'd see if the UI actually loads...it never does.
So, am I doing something wrong with the NSTimer, or are my troubles elsewhere? How can I use the debugging tools in xcode to get more information?
EXC_BAD_ACCESS usually indicates a memory management error, without seeing the code probably from somewhere else in your app. It's a very common error for beginners, but an important subject to fully understand, so I'd suggest looking through some of the questions on memory management here and find a few guides or tutorials to look through. It's actually pretty easy to learn.
Also, it shouldn't hurt but unless you need to access the timer in between fire events, you don't actually need to store it as an instance variable. Once you create and start a timer it's added to and retained by the application's run loop.
Have you got NSZombieEnabled?
Might be useful if this is failing on an over released object.