Problem recording incoming call audio on Windows

[Rac0n]

Hello,

I am new in .Net and, especially, in the SIP space. I am using this library in order to get a call from a softphone.

I managed to make the connection to receive the call. However, I am having trouble with recording it. I do get a file and some audio in it but the volume is very low and there is a lot of distortion (or noise). I would assume it is a codec problem, or a audio feature one.

This is basically my code. The softphone uses the G729 codec.

`private static readonly WaveFormat _waveFormat = new WaveFormat(8000, 16, 1);

static async Task Main()
{
var outputFolder = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyMusic), "NAudio");
Directory.CreateDirectory(outputFolder);
outputFilePath = Path.Combine(outputFolder, "output.wav");
_waveFile = new WaveFileWriter(outputFilePath, _waveFormat);

_sipTransport = new SIPTransport();
_sipTransport.AddSIPChannel(new SIPUDPChannel(new IPEndPoint(IPAddress.Any, SIP_PORT)));

_userAgent = new(_sipTransport, SIP_USERNAME, SIP_PASSWORD, $"{SIP_SERVER}:{SIP_PORT}", DEFAULT_EXPIRY);

_userAgent.RegistrationSuccessful += (uri, resp) =>
{
    Console.WriteLine($"{uri} registration succeeded.");

    Console.WriteLine(">>>>>");
    Console.WriteLine(resp.ToString());
    Console.WriteLine(">>>>>");

    _ua = new SIPUserAgent(_sipTransport, null, true);

    _ua.OnIncomingCall += async (ua, req) =>
    {
        Console.WriteLine(">>>>>");
        Console.WriteLine(req.ToString());
        Console.WriteLine(">>>>>");

        var uas = ua.AcceptCall(req);

        WindowsAudioEndPoint winAudioEP = new WindowsAudioEndPoint(new AudioEncoder());
        winAudioEP.RestrictFormats((format) => format.Codec == AudioCodecsEnum.G729);

        VoIPMediaSession voipMediaSession = new VoIPMediaSession(winAudioEP.ToMediaEndPoints());

        
        voipMediaSession.AcceptRtpFromAny = true;
        voipMediaSession.OnRtpPacketReceived += OnRtpPacketReceived;

        await Task.Delay(500);

        await ua.Answer(uas, voipMediaSession);

        if (ua.IsCallActive)
        {
            await voipMediaSession.Start();
            await winAudioEP.PauseAudioSink();
        }
    };
};

_userAgent.Start();

Console.ReadLine();
_ua.Hangup();
_waveFile?.Close();

_userAgent.Stop();
Task.Delay(1500).Wait();
_sipTransport.Shutdown();

}

private static void OnRtpPacketReceived(IPEndPoint remoteEndPoint, SDPMediaTypesEnum mediaType, RTPPacket rtpPacket)
{
if (mediaType == SDPMediaTypesEnum.audio)
{
var sample = rtpPacket.Payload;

    if (rtpPacket.Header.PayloadType == (int)SDPWellKnownMediaFormatsEnum.G729)
    {
        G729Decoder decoder = new G729Decoder();
        byte[] pcmSample = decoder.Process(sample);

        Console.WriteLine(pcmSample.Length);



        _waveFile.Write(pcmSample, 0, pcmSample.Length);
    }
    else {

        for (int index = 0; index < sample.Length; index++)
        {
            if (rtpPacket.Header.PayloadType == (int)SDPWellKnownMediaFormatsEnum.PCMA)
            {
                short pcm = NAudio.Codecs.ALawDecoder.ALawToLinearSample(sample[index]);
                byte[] pcmSample = new byte[] { (byte)(pcm & 0xFF), (byte)(pcm >> 8) };
                _waveFile.Write(pcmSample, 0, 2);
            }
            else
            {
                short pcm = NAudio.Codecs.MuLawDecoder.MuLawToLinearSample(sample[index]);
                byte[] pcmSample = new byte[] { (byte)(pcm & 0xFF), (byte)(pcm >> 8) };
                _waveFile.Write(pcmSample, 0, 2);
            }
        }
    }
}

}`

[sipsorcery]

Did you see the RecordIncomingCall example?

[Rac0n]

Hello! I did look at the example! I also managed to find the problem. I used a different codec instead of G729. I used G711 and everything worked. Thanks for the response!

[sipsorcery]

Gr8, glad you solved it.