AudioFileReadBytes from a memory block, not a file - ios

Question

I'd like to cache CAF files before converting them to PCM whenever they play.
For example,
char *mybuffer = malloc(mysoundsize);
FILE *f = fopen("mysound.caf", "rb");
fread(mybuffer, mysoundsize, 1, f);
fclose(f);
char *pcmBuffer = malloc(pcmsoundsize);
// Convert to PCM for playing
AudioFileReadBytes(mybuffer, false, 0, mysoundsize, &numbytes, pcmBuffer);
This way, whenever the sound plays, the compressed CAF file is already loaded into memory, avoiding disk access. How can I open a block of memory with an 'AudioFileID' to make AudioFileReadBytes happy? Is there another method I can use?

Answer 1

I have not done it myself, but from the documentation I would think that you have to use AudioFileOpenWithCallbacks and implement callback functions that read from your memory buffer.

Answer 2

You can finish it with AudioFileStreamOpen
fileprivate var streamID: AudioFileStreamID?
public func parse(data: Data) throws {
let streamID = self.streamID!
let count = data.count
_ = try data.withUnsafeBytes { (bytes: UnsafePointer<UInt8>) in
let result = AudioFileStreamParseBytes(streamID, UInt32(count), bytes, [])
guard result == noErr else {
throw ParserError.failedToParseBytes(result)
}
}
}
you can store the data in memory within the callback
func ParserPacketCallback(_ context: UnsafeMutableRawPointer, _ byteCount: UInt32, _ packetCount: UInt32, _ data: UnsafeRawPointer, _ packetDescriptions: Optional<UnsafeMutablePointer<AudioStreamPacketDescription>>) {
let parser = Unmanaged<Parser>.fromOpaque(context).takeUnretainedValue()
/// At this point we should definitely have a data format
guard let dataFormat = parser.dataFormatD else {
return
}
let format = dataFormat.streamDescription.pointee
let bytesPerPacket = Int(format.mBytesPerPacket)
for i in 0 ..< Int(packetCount) {
let packetStart = i * bytesPerPacket
let packetSize = bytesPerPacket
let packetData = Data(bytes: data.advanced(by: packetStart), count: packetSize)
parser.packetsX.append(packetData)
}
}
full code in github repo