How can mp3 data in memory be loaded into an AVAudioPCMBuffer in Swift? - swift

Question

I have a class method to read an mp3 file into an AVAudioPCMBuffer as follows:
private(set) var fullAudio: AVAudioPCMBuffer?
func initAudio(audioFileURL: URL) -> Bool {
var status = true
do {
let audioFile = try AVAudioFile(forReading: audioFileURL)
let audioFormat = audioFile.processingFormat
let audioFrameLength = UInt32(audioFile.length)
fullAudio = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: audioFrameLength)
if let fullAudio = fullAudio {
try audioFile.read(into: fullAudio)
// processing of full audio
}
} catch {
status = false
}
return status
}
However, I now need to be able to read the same mp3 info from memory (rather than a file) into the AVAudioPCMBuffer without using the file system, where the info is held in the Data type, for example using a function declaration of the form
func initAudio(audioFileData: Data) -> Bool {
// some code setting up fullAudio
}
How can this be done? I've looked to see whether there is a route from Data holding mp3 info to AVAudioPCMBuffer (e.g. via AVAudioBuffer or AVAudioCompressedBuffer), but haven't seen a way forward.

Answer 1

I went down the rabbit hole on this one. Here is what probably amounts to a Rube Goldberg-esque solution:
A lot of the pain comes from using C from Swift.
func data_AudioFile_ReadProc(_ inClientData: UnsafeMutableRawPointer, _ inPosition: Int64, _ requestCount: UInt32, _ buffer: UnsafeMutableRawPointer, _ actualCount: UnsafeMutablePointer<UInt32>) -> OSStatus {
let data = inClientData.assumingMemoryBound(to: Data.self).pointee
let bufferPointer = UnsafeMutableRawBufferPointer(start: buffer, count: Int(requestCount))
let copied = data.copyBytes(to: bufferPointer, from: Int(inPosition) ..< Int(inPosition) + Int(requestCount))
actualCount.pointee = UInt32(copied)
return noErr
}
func data_AudioFile_GetSizeProc(_ inClientData: UnsafeMutableRawPointer) -> Int64 {
let data = inClientData.assumingMemoryBound(to: Data.self).pointee
return Int64(data.count)
}
extension Data {
func convertedTo(_ format: AVAudioFormat) -> AVAudioPCMBuffer? {
var data = self
var af: AudioFileID? = nil
var status = AudioFileOpenWithCallbacks(&data, data_AudioFile_ReadProc, nil, data_AudioFile_GetSizeProc(_:), nil, 0, &af)
guard status == noErr, af != nil else {
return nil
}
defer {
AudioFileClose(af!)
}
var eaf: ExtAudioFileRef? = nil
status = ExtAudioFileWrapAudioFileID(af!, false, &eaf)
guard status == noErr, eaf != nil else {
return nil
}
defer {
ExtAudioFileDispose(eaf!)
}
var clientFormat = format.streamDescription.pointee
status = ExtAudioFileSetProperty(eaf!, kExtAudioFileProperty_ClientDataFormat, UInt32(MemoryLayout.size(ofValue: clientFormat)), &clientFormat)
guard status == noErr else {
return nil
}
if let channelLayout = format.channelLayout {
var clientChannelLayout = channelLayout.layout.pointee
status = ExtAudioFileSetProperty(eaf!, kExtAudioFileProperty_ClientChannelLayout, UInt32(MemoryLayout.size(ofValue: clientChannelLayout)), &clientChannelLayout)
guard status == noErr else {
return nil
}
}
var frameLength: Int64 = 0
var propertySize: UInt32 = UInt32(MemoryLayout.size(ofValue: frameLength))
status = ExtAudioFileGetProperty(eaf!, kExtAudioFileProperty_FileLengthFrames, &propertySize, &frameLength)
guard status == noErr else {
return nil
}
guard let pcmBuffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: AVAudioFrameCount(frameLength)) else {
return nil
}
let bufferSizeFrames = 512
let bufferSizeBytes = Int(format.streamDescription.pointee.mBytesPerFrame) * bufferSizeFrames
let numBuffers = format.isInterleaved ? 1 : Int(format.channelCount)
let numInterleavedChannels = format.isInterleaved ? Int(format.channelCount) : 1
let audioBufferList = AudioBufferList.allocate(maximumBuffers: numBuffers)
for i in 0 ..< numBuffers {
audioBufferList[i] = AudioBuffer(mNumberChannels: UInt32(numInterleavedChannels), mDataByteSize: UInt32(bufferSizeBytes), mData: malloc(bufferSizeBytes))
}
defer {
for buffer in audioBufferList {
free(buffer.mData)
}
free(audioBufferList.unsafeMutablePointer)
}
while true {
var frameCount: UInt32 = UInt32(bufferSizeFrames)
status = ExtAudioFileRead(eaf!, &frameCount, audioBufferList.unsafeMutablePointer)
guard status == noErr else {
return nil
}
if frameCount == 0 {
break
}
let src = audioBufferList
let dst = UnsafeMutableAudioBufferListPointer(pcmBuffer.mutableAudioBufferList)
if src.count != dst.count {
return nil
}
for i in 0 ..< src.count {
let srcBuf = src[i]
let dstBuf = dst[i]
memcpy(dstBuf.mData?.advanced(by: Int(dstBuf.mDataByteSize)), srcBuf.mData, Int(srcBuf.mDataByteSize))
}
pcmBuffer.frameLength += frameCount
}
return pcmBuffer
}
}
A more robust solution would probably read the sample rate and channel count and give the option to preserve them.
Tested using:
let url = URL(fileURLWithPath: "/tmp/test.mp3")
let data = try! Data(contentsOf: url)
let format = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 44100, channels: 1, interleaved: false)!
if let d = data.convertedTo(format) {
let avf = try! AVAudioFile(forWriting: URL(fileURLWithPath: "/tmp/foo.wav"), settings: format.settings, commonFormat: format.commonFormat, interleaved: format.isInterleaved)
try! avf.write(from: d)
}