How to record FLAC format in iOS 11+

Question

I changed the code in AudioController.swift to:

...
// Set format for mic input (bus 1) on RemoteIO's output scope
var asbd = AudioStreamBasicDescription()
...
asbd.mFormatID = kAudioFormatFLAC
asbd.mFormatFlags = kAppleLosslessFormatFlag_16BitSourceData
...

and SpeechRecognitionService.swift to

...
// send an initial request message to configure the service
let recognitionConfig = RecognitionConfig()
recognitionConfig.encoding =  .flac
...

I tried tinkering around with AudioStreamBasicDescription.mFormatFlags but cannot find the right flags for Google Speech API to recognize the format.

How do I make iOS to record FLAC using the given iOS API?

https://stackoverflow.com/questions/17906765/chunked-encoding-using-flac-on-ios — Christian Abella, Jun 21 '18 at 23:33
@ChristianAbella The link that you pinged records PCM and then converts to FLAC — Raviteja, Jun 26 '18 at 17:39
@jspcal The code just halts for a response from AudioRecorder, probably something that I did. I can't debug it since there is no error. — Raviteja, Jun 26 '18 at 17:40
@iOSGeek Any code examples or documentation links that you know of? — Raviteja, Jun 26 '18 at 17:41
please check some part of code that I have used to record audio directly in Flac format @Raviteja — iOS Geek, Jun 27 '18 at 04:12

score 1 · Answer 1 · answered Jun 27 '18 at 04:11

Try This

/// Common Struct 
struct Manager
{    
    //Required Objects - AVFoundation
    ///AVAudio Session
    static var recordingSession: AVAudioSession!

    ///AVAudio Recorder
    static var recorder: AVAudioRecorder?
}

Permissions

func CheckForPermission() {
    Manager.recordingSession = AVAudioSession.sharedInstance()
    do {
        try Manager.recordingSession.setCategory(AVAudioSessionCategoryPlayAndRecord, with: .defaultToSpeaker)
        Manager.recordingSession.requestRecordPermission({ (allowed) in
            if allowed {
                Manager.micAuthorised = true
            }
            else {
                Manager.micAuthorised = false
            }
        })
        DispatchQueue.main.async  {
            //Reload Label text in Home screen
            NotificationCenter.default.post(name: NSNotification.Name(rawValue: "updateLabel"), object: nil)
        }
    }
    catch {
        print("Failed to set Category", error.localizedDescription)
    }
}

Recorder Setting & Recording with flac

func startMainRecording() {
    print("Main Recording session is created")

    //Get unique File Name
    Manager.audioName = getUniqueName()
    let AudioFileName = getDocumentsDirectory().appendingPathComponent("\(Manager.audioName).flac")
    print("New Path: \(AudioFileName)")

    //Recorder Settings
    let settings: [String: Any] = [
        /// Format Flac
        AVFormatIDKey: Int(kAudioFormatFLAC),
        AVSampleRateKey: 16000,
        AVNumberOfChannelsKey: 1,
        AVLinearPCMBitDepthKey: 16,
        AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue,
        AVLinearPCMIsBigEndianKey: false,
        AVLinearPCMIsFloatKey: false,
        ]

    //Handler
    do {
        //Activate session when required

        //try Manager.recordingSession.setPreferredSampleRate(44000)
        try Manager.recordingSession.setActive(true)

        //Start Recording With Audio File name
        Manager.recorder = try AVAudioRecorder(url: AudioFileName, settings: settings)
        Manager.recorder?.delegate = self
        Manager.recorder?.isMeteringEnabled = true
    }
    catch
    {
        //Finish Recording with a Error
        print("Error Handling: \(error.localizedDescription)")
        /// Saved here if any error occur while recording Just case
        self.finishRecording(success: false)
    }
}

FLAC if I remember correctly needs the sample rate to be 44100, I will try this and see. — Raviteja, Jun 27 '18 at 16:59
I used a low sample rate just to keep my file smaller in size as I was required to upload in Database — iOS Geek, Jun 28 '18 at 04:14
@iOSGeek How to stop recording and is this possible to record video with flac encoded audio ? — Varun Naharia, May 15 '19 at 06:35
@iOSGeek I got moved to a different project, never really got to the bottom of this. I hope your answer will help anyone that has the same problem — Raviteja, Aug 15 '21 at 19:18

How to record FLAC format in iOS 11+

1 Answers1