iOS SoundTouch framework BPM Detection example - ios

Question

I have searched all over the web and cannot find a tutorial on how to use the SoundTouch library for beat detection.
(Note: I have no C++ experience prior to this. I do know C, Objective-C, and Java. So I could have messed some of this up, but it compiles.)
I added the framework to my project and managed to get the following to compile:
NSString *path = [[NSBundle mainBundle] pathForResource:#"song" ofType:#"wav"];
NSData *data = [NSData dataWithContentsOfFile:path];
player =[[AVAudioPlayer alloc] initWithData:data error:NULL];
player.volume = 1.0;
player.delegate = self;
[player prepareToPlay];
[player play];
NSUInteger len = [player.data length]; // Get the length of the data
soundtouch::SAMPLETYPE sampleBuffer[len]; // Create buffer array
[player.data getBytes:sampleBuffer length:len]; // Copy the bytes into the buffer
soundtouch::BPMDetect *BPM = new soundtouch::BPMDetect(player.numberOfChannels, [[player.settings valueForKey:#"AVSampleRateKey"] longValue]); // This is working (tested)
BPM->inputSamples(sampleBuffer, len); // Send the samples to the BPM class
NSLog(#"Beats Per Minute = %f", BPM->getBpm()); // Print out the BPM - currently returns 0.00 for errors per documentation
The inputSamples(*samples, numSamples) song byte information confuses me.
How do I get these pieces of information from a song file?
I tried using memcpy() but it doesn't seem to be working.
Anyone have any thoughts?

Answer 1

After hours and hours of debugging and reading the limited documentation on the web, I modified a few things before stumbling upon this: You need to divide numSamples by numberOfChannels in the inputSamples() function.
My final code is like so:
NSString *path = [[NSBundle mainBundle] pathForResource:#"song" ofType:#"wav"];
NSData *data = [NSData dataWithContentsOfFile:path];
player =[[AVAudioPlayer alloc] initWithData:data error:NULL];
player.volume = 1.0; // optional to play music
player.delegate = self;
[player prepareToPlay]; // optional to play music
[player play]; // optional to play music
NSUInteger len = [player.data length];
soundtouch::SAMPLETYPE sampleBuffer[len];
[player.data getBytes:sampleBuffer length:len];
soundtouch::BPMDetect BPM(player.numberOfChannels, [[player.settings valueForKey:#"AVSampleRateKey"] longValue]);
BPM.inputSamples(sampleBuffer, len/player.numberOfChannels);
NSLog(#"Beats Per Minute = %f", BPM.getBpm());

Answer 2

I've tried this solution to read the BPM from mp3 files (using the TSLibraryImport class to convert to wav) inside the iOS Music Library:
MPMediaItem *item = [collection representativeItem];
NSURL *urlStr = [item valueForProperty:MPMediaItemPropertyAssetURL];
TSLibraryImport* import = [[TSLibraryImport alloc] init];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSURL* destinationURL = [NSURL fileURLWithPath:[documentsDirectory stringByAppendingPathComponent:#"temp_data"]];
[[NSFileManager defaultManager] removeItemAtURL:destinationURL error:nil];
[import importAsset:urlStr toURL:destinationURL completionBlock:^(TSLibraryImport* import) {
NSString *outPath = [documentsDirectory stringByAppendingPathComponent:#"temp_data"];
NSData *data = [NSData dataWithContentsOfFile:outPath];
AVAudioPlayer *player =[[AVAudioPlayer alloc] initWithData:data error:NULL];
NSUInteger len = [player.data length];
int numChannels = player.numberOfChannels;
soundtouch::SAMPLETYPE sampleBuffer[1024];
soundtouch::BPMDetect *BPM = new soundtouch::BPMDetect(player.numberOfChannels, [[player.settings valueForKey:#"AVSampleRateKey"] longValue]);
for (NSUInteger i = 0; i <= len - 1024; i = i + 1024) {
NSRange r = NSMakeRange(i, 1024);
//NSData *temp = [player.data subdataWithRange:r];
[player.data getBytes:sampleBuffer range:r];
int samples = sizeof(sampleBuffer) / numChannels;
BPM->inputSamples(sampleBuffer, samples); // Send the samples to the BPM class
}
NSLog(#"Beats Per Minute = %f", BPM->getBpm());
}];
The strangeness is that the calculated BMP is always the same value:
2013-10-02 03:05:36.725 AppTestAudio[1464:1803] Beats Per Minute = 117.453835
No matter which track was i.e. number of frames or the buffer size (here I used 2K buffer size as for the SoundTouch example in the source code of the library).

Answer 3

For Swift 3:
https://github.com/Luccifer/BPM-Analyser
And use it like:
guard let filePath = Bundle.main.path(forResource: "TestMusic", ofType: "m4a"),
let url = URL(string: filePath) else {return "error occured, check fileURL"}
BPMAnalyzer.core.getBpmFrom(url, completion: nil)
Feel free to comment!