How to decode m4a to PCM using AVFoundation's AVAsetReader

Question

Trying to convert M4A to PCM goes well in the start. i am able to convert and read the bytes. however i am not sure if this is the correct way to do this. as i am getting 16384 bytes when i try to get the bytes in NSData.

Here is my function

func getData(sampleRef:CMSampleBufferRef) -> NSMutableData{


    let dataBuffer = CMSampleBufferGetDataBuffer(sampleRef)
    let length = CMBlockBufferGetDataLength(dataBuffer!)

    var data = NSMutableData(length: length)


     CMBlockBufferCopyDataBytes(dataBuffer!, 0, length, data!.mutableBytes)

        print(data!)// this prints 16384 bytes 



    return data!


}

this i try to convert this data to Int16

 // 3 lines below i was just testing how it converts to Int16
    let count = data!.length / sizeof(Int16)
    var array = [Int16](count: count, repeatedValue: 0)

    data!.getBytes(&array, length: data!.length)

these are my settings to decode the PCM from M4A file.

    let outputSettings = [
        AVFormatIDKey: Int(kAudioFormatLinearPCM),
        AVSampleRateKey: 44100,
        AVLinearPCMBitDepthKey:16,
        AVLinearPCMIsFloatKey:0,
        AVNumberOfChannelsKey: 1 as NSNumber,

    ]

PS. i record the file with the same settings