How do I call CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer?

Question

I\'m trying to figure out how to call this AVFoundation function in Swift. I\'ve spent a ton of time fiddling with declarations and syntax, and got this far.

Answer 1

Swift3 solution:

func loopAmplitudes(audioFileUrl: URL) {

    let asset = AVAsset(url: audioFileUrl)

    let reader = try! AVAssetReader(asset: asset)

    let track = asset.tracks(withMediaType: AVMediaTypeAudio)[0]

    let settings = [
        AVFormatIDKey : kAudioFormatLinearPCM
    ]

    let readerOutput = AVAssetReaderTrackOutput(track: track, outputSettings: settings)
    reader.add(readerOutput)
    reader.startReading()

    while let buffer = readerOutput.copyNextSampleBuffer() {

        var audioBufferList = AudioBufferList(mNumberBuffers: 1, mBuffers: AudioBuffer(mNumberChannels: 0, mDataByteSize: 0, mData: nil))
        var blockBuffer: CMBlockBuffer?

        CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
            buffer,
            nil,
            &audioBufferList,
            MemoryLayout.size,
            nil,
            nil,
            kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment,
            &blockBuffer
        );

        let buffers = UnsafeBufferPointer(start: &audioBufferList.mBuffers, count: Int(audioBufferList.mNumberBuffers))

        for buffer in buffers {

            let samplesCount = Int(buffer.mDataByteSize) / MemoryLayout.size
            let samplesPointer = audioBufferList.mBuffers.mData!.bindMemory(to: Int16.self, capacity: samplesCount)
            let samples = UnsafeMutableBufferPointer(start: samplesPointer, count: samplesCount)

            for sample in samples {

                //do something with you sample (which is Int16 amplitude value)

            }
        }
    }
}