How can I create a spectrogram from an audio file? - swift

Question

I have tried to create a spectrogram using this apple tutorial but it uses live audio input from the microphone. I want to create one from an existing file. I have tried to convert apples example from live input to existing files with no luck, so I am wondering if there are any better resources out there.
Here is how I am getting the samples:
let samples: (naturalTimeScale: Int32, data: [Float]) = {
guard let samples = AudioUtilities.getAudioSamples(
forResource: resource,
withExtension: wExtension) else {
fatalError("Unable to parse the audio resource.")
}
return samples
}()
// Returns an array of single-precision values for the specified audio resource.
static func getAudioSamples(forResource: String,
withExtension: String) -> (naturalTimeScale: CMTimeScale,
data: [Float])? {
guard let path = Bundle.main.url(forResource: forResource,
withExtension: withExtension) else {
return nil
}
let asset = AVAsset(url: path.absoluteURL)
guard
let reader = try? AVAssetReader(asset: asset),
let track = asset.tracks.first else {
return nil
}
let outputSettings: [String: Int] = [
AVFormatIDKey: Int(kAudioFormatLinearPCM),
AVNumberOfChannelsKey: 1,
AVLinearPCMIsBigEndianKey: 0,
AVLinearPCMIsFloatKey: 1,
AVLinearPCMBitDepthKey: 32,
AVLinearPCMIsNonInterleaved: 1
]
let output = AVAssetReaderTrackOutput(track: track,
outputSettings: outputSettings)
reader.add(output)
reader.startReading()
var samplesData = [Float]()
while reader.status == .reading {
if
let sampleBuffer = output.copyNextSampleBuffer(),
let dataBuffer = CMSampleBufferGetDataBuffer(sampleBuffer) {
let bufferLength = CMBlockBufferGetDataLength(dataBuffer)
var data = [Float](repeating: 0,
count: bufferLength / 4)
CMBlockBufferCopyDataBytes(dataBuffer,
atOffset: 0,
dataLength: bufferLength,
destination: &data)
samplesData.append(contentsOf: data)
}
}
return (naturalTimeScale: track.naturalTimeScale, data: samplesData)
}
And here is how I am performing the "fft" or dct in this case:
static var sampleCount = 1024
let forwardDCT = vDSP.DCT(count: sampleCount,
transformType: .II)
guard let freqs = forwardDCT?.transform(samples.data) else { return }
This is the part where I begin to get lost/stuck in the apple tutorial. How can I create the spectrogram from here?