I finally fixed this not appending the Buffers to an array and writing the audio file later but rather setting up an audio-writer class that takes samples in real time and writes them to a file. For anybody who is facing the same problem, here is my class (probably very poorly and inefficiently written, so beware xD):
public class audioWriter: ObservableObject{
var assetWriter: AVAssetWriter
var audioInput: AVAssetWriterInput
init(assetWriter: AVAssetWriter, audioInput: AVAssetWriterInput) {
self.assetWriter = assetWriter
self.audioInput = audioInput
}
func startWriting(firstBuffer: CMSampleBuffer){
audioInput.expectsMediaDataInRealTime = true
assetWriter.add(audioInput)
assetWriter.startWriting()
assetWriter.startSession(atSourceTime: CMSampleBufferGetPresentationTimeStamp(firstBuffer))
}
func addSample(sample: CMSampleBuffer){
audioInput.append(sample)
}
func finish(){
audioInput.markAsFinished()
assetWriter.finishWriting{}
}
}
The class is then called like this:
func startAudio(url: URL){
let audioOutputSettings: [String: Any] = [
AVFormatIDKey: kAudioFormatLinearPCM,
AVSampleRateKey: 44100.0,
AVNumberOfChannelsKey: 1,
AVLinearPCMBitDepthKey: 16,
AVLinearPCMIsBigEndianKey: false,
AVLinearPCMIsFloatKey: false,
AVLinearPCMIsNonInterleaved: false
]
let assetWriter = try? AVAssetWriter(outputURL: url, fileType: AVFileType.wav)
let audioInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: audioOutputSettings)
recorder = audioWriter(assetWriter: assetWriter!, audioInput: audioInput)
recorder?.startWriting(firstBuffer: buffer!)
recording = true
}
The recording = true is for my session func in the ARSessionObserver I am also using to call the startAudio function:
func session( _ session: ARSession, didOutputAudioSampleBuffer audioSampleBuffer: CMSampleBuffer){
buffer = audioSampleBuffer
if recording{
print("Audio Sample: \(count)")
count += 1
let newBuffer = try? CMSampleBuffer(copying: buffer!)
recorder?.addSample(sample: newBuffer!)
}
}
I am not sure if I need the detour of copying the buffer before writing it to my audio file with let newBuffer = try? CMSampleBuffer(copying: buffer!) , if anybody knows more, please do tell : )
This has worked for me, but if anyone comes up with a more efficient way, feel free to share :D
