Using NSURLSession to play remote audio, code critique - ios

Question

First, to avoid posting a great deal of code on here, I have created a very basic example of what I am after - https://github.com/opheliadesign/AudioTest.
I am brand new to iOS development and I'm having a little trouble understanding the best way to load and play a static MP3 file on a remote server. The audio is not streaming live, is less than a megabyte - about 30 seconds long in average (they are radio dispatches).
It has been suggested that I use NSURLSession to load the MP3 file and then play it within the completion block. This seems to be working but I have a feeling that I could be handling it better, just do not know how. Here is the block where I grab the audio and begin playing:
-(void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:YES];
NSLog(#"View loaded");
// Register to receive notification from AppDelegate when entering background
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(stopPlayingAudio) name:#"stopPlayingAudio" object:nil];
// Assign timer to update progress
self.updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:#selector(updateSeekBar) userInfo:nil repeats:YES];
// Demo recording URL
NSString *recordingUrl = #"https://s3.amazonaws.com/tevfd-recording/All_Fire_and_EMS_2015-02-0214_48_33_630819.mp3";
NSURLSession *session = [NSURLSession sharedSession];
[[session dataTaskWithURL:[NSURL URLWithString:recordingUrl] completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
if (!error) {
NSLog(#"No error..");
self.player = [[AVAudioPlayer alloc]initWithData:data error:nil];
// Setup slider for track position
self.slider.minimumValue = 0;
self.slider.maximumValue = self.player.duration;
[self.player prepareToPlay];
[self.player play];
}
}]resume];
}
For example, have a slider that updates the player's position when it is moved. I initialize the AVAudioPlayer in the completion block but create a property for it in the header. If the player has not been initialized, could moving the slider cause a crash? If so, how should I handle this better?
Also, I have a timer that updates the slider position as the AVAudioPlayer plays. When the track reaches its end, the timer continues - clearly this is a potential memory issue. Not sure of the best way to handle this and I would also like for the user to be able to start playing the recording again after it is completed, for example if they moved the slider to the right.
I have searched and searched, cannot seem to find anything related to specifically what I am doing. Any help would be greatly appreciated.
UPDATE
This is what I first began with but I experienced some lag between clicking on a UITableView cell and presenting the view that loaded/played the audio. Several suggested NSURLSession.
- (void)viewDidLoad {
[super viewDidLoad];
// Get the URL
NSURL *callAudioURL = [NSURL URLWithString:[self.call objectForKey:#"url"]];
NSData *callAudioData = [NSData dataWithContentsOfURL:callAudioURL];
AVAudioPlayer *audio = [[AVAudioPlayer alloc] initWithData: callAudioData error:nil];
self.player = audio;
self.slider.minimumValue = 0;
self.slider.maximumValue = self.player.duration;
[[self player] play];
self.updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:#selector(updateSeekBar) userInfo:nil repeats:YES];
}

Answer 1

If you're concerned about a small delay, then downloading and caching it is the best solution. You need to download the audio file and then play it locally. Typically playing -- or streaming -- from the network is useful only when the audio is so unique that you cannot store it locally.
To implement something like this (code untested):
-(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
NSFileHandle *hFile = [NSFileHandle fileHandleForWritingAtPath:self.localPath];
//did we succeed in opening the existing file?
if (!hFile) { //nope->create that file!
[[NSFileManager defaultManager] createFileAtPath:self.localPath contents:nil attributes:nil];
//try to open it again...
hFile = [NSFileHandle fileHandleForWritingAtPath:self.localPath];
}
//did we finally get an accessable file?
if (!hFile) {
NSLog("could not write to file %#", self.localPath);
return;
}
#try {
//seek to the end of the file
[hFile seekToEndOfFile];
//finally write our data to it
[hFile writeData:data];
} #catch (NSException * e) {
NSLog("exception when writing to file %#", self.localPath);
result = NO;
}
[hFile closeFile];
}
When all of the data has been received, start your audio:
self.player = [[AVAudioPlayer alloc] initWithContentsOfURL:self.localPath error:nil];