Swift - writeFromBuffer callback?

Question

I'm reading audio data from a PCM file (into a buffer) and writing this into a new fresh file created.

Everything works fine, but i need to know when the buffer has been written completely into the new file and I can't find a way to do it.

    //Open/Create a new file with specific Audio settings
    let audioFile = AVAudioFile(forWriting: fileUrl, settings: settings, error: &error)

    //Write buffer into the file just created
    if(audioFile.writeFromBuffer(buffer, error: &error)) {
        println("done")
    }

When i get the "done" message the file is not entirely written yet (since i'm getting format errors from another function), but if i wait for some seconds everything is just fine.

Is there a way to know when the writeFromBuffer finished?

I have tried reading the frameLength from the buffer and from the output file, they are different, probabily because the format of the buffer is different from the format of the new file that I am creating.

println("buffer frameCapacity \(buffer.frameCapacity)")
println("buffer framelength \(buffer.frameLength)")
println("audioFile length \(audioFile.length)")
println("audioFile framePosition \(audioFile.framePosition)")

the output of this is:

buffer frameCapacity 161408
buffer framelength 161408
audioFile length 88064
audioFile framePosition 88064

Any ideas? Thanks!