iOS SoundTouch framework BPM Detection example

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)

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