I have searched far and wide for documentation on how to record audio in the background and have come to the conclusion that specifying 'audio' in the plist file might work. But, because iOS 4 will terminate background apps when it runs low on memory, we must also take some steps to reduce our memory usage when we transition to the background. How do we reduce our memory usage?
Also, does anybody know a sure shot way of recording audio in the background on iOS??
I unchecked the box in the Info.plist file that says "Application does not run in background" and also added the
<key> UIBackgroundModes </ key> < array> < string> audio</ string></ array>
in Info.plist. But, the recording stops as soon as I press the "HOME" button.
What callbacks do we implement to know that application has gone to background?
Please advise.
Just in case anyone else is looking for an answer here, I got mine working by adding the UIBackgroundModes array to the plist, adding 'audio' as Item 0.
I free up all memory/controllers on exit as you would by quitting the app anyhow so all that is left are the buffers the app uses (I've allocated around 1Mb though which makes me a little nervous however it seems to have worked!) I guess reducing the fidelity would help too but it seems to work as is.
In my core Audio setup I had to either change the buffer size from 1024 to 4096 or explicitly set the buffer size... I opted for the latter as latency was an issue.
NSTimeInterval iobuffersize = (float)1024.0f/SAMPLE_RATE);
sizeofdata = sizeof(iobuffersize);
AudioSessionSetProperty(kAudioSessionProperty_PreferredHardwareIOBufferDuration, &sizeofdata, &iobuffersize);
I also had to make sure that it didn't kill the app on exit via not enabling the 'Does not run in background' option however this should be off by default anyhow.
So guess I'm answering this for peace of mind for anyone else that it does work with not much setup after all.
I am however experiencing problems with Bluetooth setup, I guess that's because the buffer sizes change again but can't figure this one out... just get -50 = invalid property warning when rendering the data via the recordingCallback. I'm guessing it's the freq/sample size but who knows... will look later but seems like background now works.
Apart from specifying background recording in the plist file, we can implement applicationDidEnterBackground wihch will tell us when the application enters background. Here, we should stop any updates to the UI because that consumes memory for eg, updating a timer and an equalizer.
The call applicationWillEnterForeground will be called just before the app returns to foreground so we can resume whatever we stopped.
The recording then takes place in the background. It would also help to implement an interruption listener(this would work in the backgroud as well) so that you don't lose your recordings.
Related
I would like to present an alert if the sound is 0.
I found this library https://github.com/moshegottlieb/SoundSwitch, but it doesn't seem to work. At least not on a simulator
Have you seen this question? They give various answers:
float vol = [[AVAudioSession sharedInstance] outputVolume];
NSLog(#"output volume: %1.2f dB", 20.f*log10f(vol+FLT_MIN));
Nonetheless it doesn't seems to work using the simulator (I'm trying and it always return the same value). This lead me to think maybe it's not something we can check from the simulator. Can you try on a real device? Let me know if it works.
EDIT: Ok so reading about it it seems there's no API avaiable to check silent mode. Anyway what people have found a workaround: Playing a short audio with no volume. If the time when it finishes (minus time when it started) is lower than the actual length of the audio is on mute mode (being in the silent mode the audio will last 0 seconds).
So, here somebody posted a class that do that for you. Let me know if it works
I'm trying to reach the file which I was downloading earlier by NSURLSession. It seems I can't read the location of the file, even though I'm doing it before delegate method ends (as the file is temporary).
Still, I'm getting nil when trying to access the data under location returned from NSURLSession delegate and error 257.
The code goes as following:
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location {
NSError *movingError = nil;
NSData *fileData = [NSData dataWithContentsOfFile:location.path options:0 error:&movingError]; // is nil
NSLog(#"%#", movingError); // is error 257
}
What's wrong with this code..? I saw similar questions NSURLSessionDownloadTask - downloads but ends with error and iPhone - copying a file from resources to Documents gives an error but these completely doesn't apply to my case.
-- edit --
I've created a new project and pasted the very same code. It works... So:
1) In my project I'm receiving error 257, probably some configuration of the project is invalid or the fact I'm using backgroundTasks somewhere else in the app messes things up
2) Same as in 1 happens if I put the source files of this download to the external framework linked in by Carthage
3) On demo project I created (copy-pasted files used in 1 & 2) everything works corretly.
If someone has an idea what can cause the fact it isn't working - would be awesome.
Late to the discussion, but I've seen the same/similar issue and investigated.
With my investigation, what you are seeing is expected (should I say “it's observed”?).
But since I'm not 100% sure how you are using URL session, I put down below what I'm trying to do, followed by my observations (important ones only).
Also, I created a sample project and put it here as downLoader.zip. You can play and check how URL session background download works. But It's better to read thru below before trying to play, though this is fairly a long note.
A. what I'm trying to do
I'm developing kind a map app, where I need to download 1000+ of small size (0.5-150kB, mostly ~20kB) PNG files at a time. Total download size of them is ~50MB, and it takes a couple of minutes to download all of them. I think that keeping users to my app just waiting for download is bad design, so I made the app to use URL Session’s background download.
I have to admit, however, that Apple’s doc says that “Background sessions are optimized for transferring a small number of large resources that can be resumed as necessary.” So, the way I’m using background session is totally opposite. But, anyway...
B. what I've observed
Below, I’ve listed my observations and my guess of why. I should say guess since they are not documented.
(1) observation: sometimes, files that should come with didFinishDownlaodingTo don’t exist.
Temporary files are put at:
/var/mobile/Containers/Data/Application/randomHexString/Library/Caches/com.apple.nsurlsessiond/Downloads/yourName.yourApp. The randomHexString changes from app’s run to run. When the files don’t exist, the randomHexString that came with didFinishDownloadingTo is the one from the “previous” session. Now, “previous” here means the session at app’s previous run !, which clearly doesn't exist at the current session at current run.
There's another scenario for non-existent file, which is that the randomHexString is ok, but the files don't exist. This seems to happen after session cancel is requested (invalidateAndCancel) and before session becomes invalid (didBecomeInvalidWithError).
Guess: This happens especially on the development phase since we terminate the app while downloading, manually or by debugger or just by bug. It seems once the download requests are handed and accepted to the OS, the OS handles our requests even after the app quits. Note we can’t know if the OS has definitely accepted the requests or not. Even after the return from URLSessionDownloadTask:resume(), sometimes files don’t exit at the next launch and sometimes they do.
Workaround: If files don’t exist, just ignore them. In a while, “this time’s” files should come.
(2) observation: sometimes, the duplicated (same) files come with didFinishDownloadingTo.
My app converts downloaded PNG files to other format. W/in didFinishDownlaodingTo, I move temp files (== OS designated) to another my app’s directory, then spawn thread (GCD) to convert the format and delete downloaded temp files. So, the other thread (didFinishDownlaodingTo) to overwrite is an issue.
Workaround: I make list of URLSessionTask:taskIdentifier and w/in didFinishDownlaodingTo, check the duplication by retrieving the taskID list to ignore duplicated files.
(3) observation: even after the user terminated the app, OS relaunches the app again.
After the user terminated the app from task switcher, quite often, the OS relaunches the app w/ application:handleEventsForBackgroundURLSession:completionHandler.
Note the sequence of relaunch is that didFinishLaunchingWithOptions comes first as regular launch, then handleEventsForBackgroundURLSession comes next.
From user’s POV, when he/she terminated the app, that’s it, done! It looks strange even after they terminated the app, it relaunches in itself and notifies something to them. It's like a zombie.
Guess: The Apple’s document says “If the user terminates your app, the system cancels any pending tasks”. The definition of “pending tasks” is not clearly stated but I understand this is from iOS POV and not user’s or program developer’s. As guessed in (1), iOS seemed to have accepted the download requests, and they are not “pending tasks” anymore.
Workaround: I create a “flagFile” after all of download requests are handed to iOS w/ URLSessionDownloadTask:resume(), of which file means that “download is ongoing”. When users terminate the app, at UIApplicationDelegate:applicationWillTerminate, I delete the flag file. Or, if all of download requests not handed to iOS, there's no flag file. Then at app’s relaunch at UIApplicationDelegate:handleEventsForBackgroundURLSession, I check if we have the flag file. If missing, then I can assume that users terminated. Two choices here. Choice-1: I will not recreate URL session. What happens next is that iOS will terminate my app in about 20 seconds. I have no idea if this (== not creating the URL session) is a legal operation but it works. Users can launch w/in this 20 sec, so I put some more code to handle that scenario. Choice-2: I create URL session. What happens next is that iOS calls delegate methods didFinishDownlaodingTo/didCompleteWithError, followed by urlSessionDidFinishEvents. If I don't do anything here, the process (app) keeps alive indefinitely w/o any notification to users: nothing in task switcher. This is nothing more than waste of memory. The option here is to fire local notification and let users know of my app, so that they can go back to my app and can terminate (Again!), though my app clearly appears as a zombie. One issue for both choices: applicationWillTerminate may not be called in certain situation (though I've yet confirmed). At this case, flag file is left as regular ops and show zombie to users. So, the flag file method is just mitigation to the issue, but I think it works most of the time for my app.
Note the app is relaunched sometimes when it's killed by xcode debugger or killed by OS w/ bug (SEGFALUT).
(4) observation: after the app is terminated (by user, etc.) then relaunched by OS, the app is occasionally in active state (UIApplication.shared.applicationState is .active).
I want to notify the user on the download completion by local notification, but since it's active, local notification doesn't fire. So, I need to use UIAlertController instead. Therefore, I can't provide consistent user experience, and should look strange for users: most of the time local notification and very occasionally UIAlert. Note when app started in active state, it appears in task switcher.
Guess: totally no idea how this can happen. One good(?) thing is this happens only occasionally.
Workaround: seems none.
(5) observation: handleEventsForBackgroundURLSession/urlSessionDidFinishEvents is called just once.
I start the download after started background task (application.beginBackgroundTask). Then in expiration handler of beginBackgroundTask, I call endBackgroundTask. I don't know exactly why, but after endBackgroundTask, my process is still given lots of process time, so I can keep requesting download. This might be because download files keep coming w/ didFinishDownlaodingTo. To be a good citizen, I suspend to request further download, and fire local notification to user to put the app to foreground. Now, once I suspend the request, in 4-5 seconds, OS determines the URL session is over and handleEventsForBackgroundURLSession then urlSessionDidFinishEvents are called. This is one-off event. When the user put the app in foreground to resume download, then put it again in background, no handleEventsForBackgroundURLSession/urlSessionDidFinishEvents will come anymore. What's unclear to me is the definition of session's start and end. It seems the session starts at first URLSessionTask.resume(), then ends w/ timeout, which seems to be determined by URLSessionConfiguration.timeoutIntervalForRequest. However, setting large number here (1000 sec) doesn't affect anything, it's always 4-5 seconds.
Guess: no idea
Workaround: don't relay on urlSessionDidFinishEvents while the app is alive. Relay only when app relaunched by OS and at initial handleEventsForBackgroundURLSession/urlSessionDidFinishEvents.
===============
Below, I listed about the sample project (downLoader.zip). You can verify all of above with the sample.
The app has a list of download files. The number of files is 1921, and 56MB in total. They are 256x256 PNG map tile files that are located in a server managed by Geo Spatial Information Authority of Japan (GSI). After downloaded, they are moved to Library/Cache/download. If your device is jail-broken, you can view them w/ Filza.
crash itself to test relaunch
emulate background task expiration
logging to file since debugger doesn't work after relaunch by OS. The file is in Documents, can be moved to PC.
Do play with the real device. Simulator doesn't relaunch the app.
Project built w/ Xcode 8.3.3 and tested w/ iphone6+/9.3.3 and iphone7+/10.3.1
To see if app relaunched w/ xcode, go to Debug/Attach to Process menu and see if downLoader is listed.
===============
I think URL session background download behaves trickily, especially at relaunch. We need to consider at least the observations I listed above, or the app users will get confused.
I found same error code 257 from online users feedback.In the error scene, the location always refers to a strange bundle identifier:com.sdyd.SDMobileMixSmart. And I guess this's an apple system bug.
I am using the MPMoviePlayerController(MPMPC) to stream audio into an application and thats working really fine. Just with one exception, during low network connectivity the app becomes unresponsive.
Now I have even tried to use AVPlayer too but with more or less same experience. And for some reason I cannot find any issues related to this on the internet. So I am not sure if this is from my end or is it how MPMoviePlayerController behaves during low connectivity.
I even tried to log any function that is being called after giving URL to the MPMPC but none of the functions are called.
I have used below three notification to get events of the MPMPC
MPMoviePlayerLoadStateDidChangeNotification
MPMoviePlayerPlaybackDidFinishNotification
MPMoviePlayerPlaybackStateDidChangeNotification
Once the available networking bandwidth is becoming too low to keep up proper playback, MPMoviePlayerController will trigger the MPMoviePlayerLoadStateDidChangeNotification and the loadState will have MPMovieLoadStateStalled set.
You may then mask the load-state within your notification handler and run any actions needed by your app for this state:
if ((movieController_.loadState & MPMovieLoadStateStalled) == MPMovieLoadStateStalled)
{
NSLog(#"playback stalled - make sure we don't block now!");
}
Once the player has recovered, once again the MPMoviePlayerLoadStateDidChangeNotification is triggered and the loadState property will have the bits for MPMovieLoadStatePlaythroughOK set:
if ((movieController_.loadState & MPMovieLoadStatePlaythroughOK) == MPMovieLoadStatePlaythroughOK)
{
NSLog(#"playback should run uninterrupted from now on.");
}
However, I never experienced any interface slowdowns of my app caused by the MPMovieLoadStateStalled state. I'ld say that must be your code acting weird, it is not MPMoviePlayerController as I know it. Additionally, those notifications are always sent, I never experienced scenarios in which they were not properly triggered.
I can only recommend to recreate this issue within a minimal test-case and work your way up from that one towards your app (possibly from both sides, test-case and your app).
For simulating bandwidth breakdowns, I would recommend using Charles proxy.
I want to exit my application programatically, I googled, some people suggesting to use exit(1), but apple is not supporting that I guess. If it is the case, How do I exit my application programatically. Any helps appreciated.
exit(0); will work but don't use it
You shouldn't force close an app as the standard way to terminate an application is to press the home button (or use the multitasking bar)
Don’t Quit Programmatically
Never quit an iOS application programmatically because people tend to
interpret this as a crash. However, if external circumstances prevent
your application from functioning as intended, you need to tell your
users about the situation and explain what they can do about it.
Depending on how severe the application malfunction is, you have two
choices.
Display an attractive screen that describes the problem and suggests a
correction. A screen provides feedback that reassures users that
there’s nothing wrong with your application. It puts users in control,
letting them decide whether they want to take corrective action and
continue using your application or press the Home button and open a
different application
If only some of your application's features are not working, display
either a screen or an alert when people activate the feature. Display
the alert only when people try to access the feature that isn’t
functioning.
Source
I believe u are not reading the comment properly thus posting the answer for ur question here:
"Simply Don't do that. as apple does not allow application to crash like that."
look at here. How do I exit my iOS app gracefully after handling a Local Notification and here Exit application in iOS 4.0 there are fare discussion over here.
After the release of iOS4, multitasking(new feature) was added by APPLE. This feature enabled the users to keep the app into suspended state in the background if in between he has to do some other activity(e.g. picking up phone call). So Apple considers your app should be maintained in the background until the user deletes the application from the background. And after this if you want to exit use exit(0);, using this would further lead to rejection from AppStore
Here's a wrong way to accomplished exit function in your app. This is coming to mind when I read your question, never applied anywhere, so be careful if you'll gonna implement this!
- (void) exitApp
{
NSArray *array = [[[NSArray alloc] init] autorelease];
NSLog(#"%#",[array objectAtIndex:10]); //will crash here, looks like exit.
}
P.S. You can put this code inside your UIAlertView asking exit confirmation like Do you really want to exit?. In YES button pressed you can call [self exitApp]; User think that he'll exit from the app.
I'm setting up an AVAudioSession when the app launches and setting the delegate to the appDelegate. Everything seems to be working (playback, etc) except that beginInterruption on the delegate is not being called when the phone receives a call. When the call ends endInterruption is being called though.
The only thought I have is that the audio player code I'm using used to be based on AVAudioPlayer, but is now using AVPlayer. The callbacks for the AVAudioPlayer delegate for handling interrupts are still in there, but it seems odd that they would conflict in any way.
Looking at the header, in iOS6, it looks like AVAudioSessionDelegate is now deprecated.
Use AVAudioSessionInterruptionNotification instead in iOS6.
Update: That didn't work. I think there's a bug in the framework.
Yes, in my experience, beginInterruption, nor the newly documented AVAudioSessionInterruptionNotification work properly. What I had to do was track the status of the player using a local flag, then handle the endInterruption:withFlags: method in order to track recovery from interruptions.
With iOS 6, the resuming from an interruption will at least keep your AudioPlayer in the right place, so there was no need for me to store the last known play time of my AVAudioPlayer, I simply had to hit play.
Here's the solution that I came up with. It seems like iOS 6 kills your audio with a Media Reset if an AVPlayer stays resident too long. What ends up happening, is the AVPlayer plays, but no sound comes out. The rate on the AVPlayer is 1, but there's absolutely no sound. To add pain to the situation, there's no error on either the AVAudioSession setActive, nor the AVPlayer itself that indicates that there's a problem.
Add to the fact that you can't depend on appWillResignActive, because your app may already be in the background if you're depending on remote control gestures at all.
The final solution I implemented was to add a periodic observer on the AVPlayer, and record the last known time. When I receive the event that I've been given back control, I create a new AVPlayer, load it with the AVPlayerItem, and seekToTime to the proper time.
It's quite an annoying workaround, but at least it works, and avoids the periodic crashes that were happening.
I can confirm that using the C api, the interruption method is also not called when the interruption begins; only when it ends
(AudioSessionInitialize (nil, nil, interruptionListenerCallback, (__bridge void *)(self));
I've also filed a bug report with apple for the issue.
Edit: This is fixed in iOS 6.1 (but not iOS 6.0.1)
Just call:
[[AVAudioSession sharedInstance] setDelegate: self];
I just checked on my iPhone 5 (running iOS 6.0) by setting a breakpoint in the AudioSessionInterruptionListener callback function that was declared in AudioSessionInitialize(), and this interrupt callback does, in fact, get called when the app has an active audio session and audio unit and is interrupted with an incoming phone call (Xcode shows the app stopped at the breakpoint at the beginning of the interruption, which I then continue from).
I have the app then stop its audio unit and de-activate its audio session. Then, on the end interruption callback, the app re-activates the audio session and restarts the audio unit without problems (the app is recording audio properly afterwards).
I built a brand new audio streaming (AVPlayer) application atop iOS 6.0.x and found the same problem.
Delegates are now deprecated and we have to use notifications, that's great, however here's my findings:
During an incoming phone call I get only AVAudioSessionInterruptionTypeEnded in my handler, along with AVAudioSessionInterruptionOptionShouldResume. Audio session gets suspended automatically (audio fades) and I just need to resume playback of AVPlayer.
However when attempting to launch a game, such as CSR Racing, I oddly get the dreaded AVAudioSessionInterruptionTypeBegan but no sign when my application can resume playback, not even killing the game.
Now, this may depend on other factors, such as my audio category (in my case AVAudioSessionCategoryPlayback) and the mixing settings of both applications (kAudioSessionProperty_OverrideCategoryMixWithOthers), I'm not sure, but definitely I see something out of place.
Hopefully others reported that on 6.1beta this is fixed and I yet have to upgrade, so we'll see.