In iOS, How to create audio file(.wav, .mp3) file from data? - ios

Question

I am working on BLE project where hardware records the audio data & sending to the iOS application. I writting a logic to convert mp3/wav file from data.
Here, I written mp3 file conversion logic from Data like below:
func storeMusicFile(data: Data) {
let fileName = "Record-1"
guard mediaDirectoryURL != nil else {
print("Error: Failed to fetch mediaDirectoryURL")
return
}
let filePath = mediaDirectoryURL!.appendingPathComponent("/\(fileName).mp3")
do {
try data.write(to: filePath, options: .atomic)
} catch {
print("Failed while storing files.")
}
}
But while playing an audio file in AVAudioPlayer, I am getting "The operation couldn’t be completed. (OSStatus error 1954115647.)" error.
So, Confused whether audio file conversion logic is wrong or data from hardware is still needs to decode?

Answer 1

The previous answer from #sagar-thummar saved me a ton of time. Unfortunately I am not allowed to vote or comment on it.
A few corrections I need to do was:
change mediaDirectoryURL to documentDirectoryURL
create ARError exception
adjust the sample rate AND bits per sample to my settings

Answer 2

To create a audio file(.mp3/.wav), you have to dynamically calculate header file data & need to append that header with actual transfer audio data from the hardware.
Reference: WAVE PCM soundfile format
Here, below I added Swift 4 code snippet for reference
//MARK: Logic for Creating Audio file
class ARFileManager {
static let shared = ARFileManager()
let fileManager = FileManager.default
var documentDirectoryURL: URL? {
return fileManager.urls(for: .documentDirectory, in: .userDomainMask).first
}
func createWavFile(using rawData: Data) throws -> URL {
//Prepare Wav file header
let waveHeaderFormate = createWaveHeader(data: rawData) as Data
//Prepare Final Wav File Data
let waveFileData = waveHeaderFormate + rawData
//Store Wav file in document directory.
return try storeMusicFile(data: waveFileData)
}
private func createWaveHeader(data: Data) -> NSData {
let sampleRate:Int32 = 2000
let chunkSize:Int32 = 36 + Int32(data.count)
let subChunkSize:Int32 = 16
let format:Int16 = 1
let channels:Int16 = 1
let bitsPerSample:Int16 = 8
let byteRate:Int32 = sampleRate * Int32(channels * bitsPerSample / 8)
let blockAlign: Int16 = channels * bitsPerSample / 8
let dataSize:Int32 = Int32(data.count)
let header = NSMutableData()
header.append([UInt8]("RIFF".utf8), length: 4)
header.append(intToByteArray(chunkSize), length: 4)
//WAVE
header.append([UInt8]("WAVE".utf8), length: 4)
//FMT
header.append([UInt8]("fmt ".utf8), length: 4)
header.append(intToByteArray(subChunkSize), length: 4)
header.append(shortToByteArray(format), length: 2)
header.append(shortToByteArray(channels), length: 2)
header.append(intToByteArray(sampleRate), length: 4)
header.append(intToByteArray(byteRate), length: 4)
header.append(shortToByteArray(blockAlign), length: 2)
header.append(shortToByteArray(bitsPerSample), length: 2)
header.append([UInt8]("data".utf8), length: 4)
header.append(intToByteArray(dataSize), length: 4)
return header
}
private func intToByteArray(_ i: Int32) -> [UInt8] {
return [
//little endian
UInt8(truncatingIfNeeded: (i ) & 0xff),
UInt8(truncatingIfNeeded: (i >> 8) & 0xff),
UInt8(truncatingIfNeeded: (i >> 16) & 0xff),
UInt8(truncatingIfNeeded: (i >> 24) & 0xff)
]
}
private func shortToByteArray(_ i: Int16) -> [UInt8] {
return [
//little endian
UInt8(truncatingIfNeeded: (i ) & 0xff),
UInt8(truncatingIfNeeded: (i >> 8) & 0xff)
]
}
func storeMusicFile(data: Data) throws -> URL {
let fileName = "Record \(Date().dateFileName)"
guard mediaDirectoryURL != nil else {
debugPrint("Error: Failed to fetch mediaDirectoryURL")
throw ARError(localizedDescription: AlertMessage.medioDirectoryPathNotAvaiable)
}
let filePath = mediaDirectoryURL!.appendingPathComponent("\(fileName).wav")
debugPrint("File Path: \(filePath.path)")
try data.write(to: filePath)
return filePath //Save file's path respected to document directory.
}
}