Repeating Audio in WatchKit (AVAudioPlayer?)?

Question

I am wanting to loop a local audio file in my Apple Watch App. Currently I am using AVAudioPlayerNode and AVAudioEngine which works well but I cannot figure out how to loop the sound.

I noticed that I can use AVAudioPlayer, which has the handy "numberOfLoops" but, for some reason AVAudioPlayer is not working on the watch. I have no idea why.

Here is my current code to play a sound:

_audioPlayer = [[AVAudioPlayerNode alloc] init];
_audioEngine = [[AVAudioEngine alloc] init];
[_audioEngine attachNode:_audioPlayer];

AVAudioFormat *stereoFormat = [[AVAudioFormat alloc] initStandardFormatWithSampleRate:44100 channels:2];
[_audioEngine connect:_audioPlayer to:_audioEngine.mainMixerNode format:stereoFormat];

if (!_audioEngine.isRunning) {
    NSError* error;
    [_audioEngine startAndReturnError:&error];
}

NSError *error;
NSBundle* appBundle = [NSBundle mainBundle];
NSURL *url = [NSURL fileURLWithPath:[appBundle pathForResource:@"FILE_NAME" ofType:@"mp3"]];
AVAudioFile *asset = [[AVAudioFile alloc] initForReading:url error:&error];

[_audioPlayer scheduleFile:asset atTime:nil completionHandler:nil];
[_audioPlayer play];

Here is the code i've tried to use for AVAudioPlayer, but does not work:

NSError *audioError;
AVAudioPlayer* player = [[AVAudioPlayer alloc] initWithContentsOfURL:[NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"FILE_NAME" ofType:@"mp3"]] error:&audioError];
player.numberOfLoops = MAXFLOAT;
player.delegate = self;
[player play];

I am using WatchKit 5.0(+).

Answer 1

If your audio file fits into memory, you could schedule playback as an AVAudioBuffer with the AVAudioPlayerNodeBufferLoops option (N.B. only tested on simulator!):

AVAudioFormat *outputFormat = [_audioPlayer outputFormatForBus:0];

__block AVAudioPCMBuffer *srcBuffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:asset.processingFormat frameCapacity:(AVAudioFrameCount)asset.length];

if (![asset readIntoBuffer:srcBuffer error:&error]) {
    NSLog(@"Read error: %@", error);
    abort();
}

AVAudioPCMBuffer *dstBuffer = [[AVAudioPCMBuffer alloc] initWithPCMFormat:outputFormat frameCapacity:(AVAudioFrameCount)asset.length];

AVAudioConverter *converter = [[AVAudioConverter alloc] initFromFormat:srcBuffer.format toFormat:dstBuffer.format];
AVAudioConverterOutputStatus status = [converter convertToBuffer:dstBuffer error:&error withInputFromBlock:^AVAudioBuffer * _Nullable(AVAudioPacketCount inNumberOfPackets, AVAudioConverterInputStatus * _Nonnull outStatus) {
    if (srcBuffer) {
        AVAudioBuffer *result = srcBuffer;
        srcBuffer = NULL;
        *outStatus = AVAudioConverterInputStatus_HaveData;
        return result;
    } else {
        *outStatus = AVAudioConverterInputStatus_EndOfStream;
        return NULL;
    }
}];

assert(status != AVAudioConverterOutputStatus_Error);

[_audioPlayer scheduleBuffer:dstBuffer atTime:nil options:AVAudioPlayerNodeBufferLoops completionHandler:nil];
[_audioPlayer play];

Answer 2

You can loop your AVAudioFile by recursively scheduling it:

__block __weak void (^weakSheduleFile)(void);
void (^scheduleFile)(void);

weakSheduleFile = scheduleFile = ^{ [self->_audioPlayer scheduleFile:asset atTime:nil completionHandler:weakSheduleFile]; };

scheduleFile();

I'm not sure if this will be a seamless loop. If it's not, you can try always having two files scheduled:

scheduleFile();
scheduleFile();