Opusdec.exe unble to decode from stdin to stdout

Question

I'm trying to encode and decode opus data using opusdec in c#.

using NAudio.Wave;
using System.Diagnostics;

List<byte[]> samples = new List<byte[]>();
WaveInEvent waveIn = new WaveInEvent();
WaveOutEvent waveOut = new WaveOutEvent();
waveIn.WaveFormat = WaveFormat.CreateIeeeFloatWaveFormat(48000, 2);
waveIn.BufferMilliseconds = 50;
var writer = new WaveFileWriter("output.wav", waveIn.WaveFormat);
waveIn.DataAvailable += (sender, e) =>
{
    using (MemoryStream m4 = new MemoryStream())
    using (var reader = new RawSourceWaveStream(new MemoryStream(e.Buffer, 0, e.BytesRecorded), waveIn.WaveFormat))
    //using (var conversionStream = new WaveFormatConversionProvider(waveIn.WaveFormat, reader))
    {
        writer.Write(e.Buffer, 0, e.BytesRecorded);
        WaveFileWriter.WriteWavFileToStream(m4, reader);
        m4.Seek(0, SeekOrigin.Begin);
        ProcessStartInfo startInfo = new ProcessStartInfo
        {
            FileName = "opusenc.exe",
            Arguments = "--quiet --speech --bitrate 160 - -",
            RedirectStandardInput = true,
            RedirectStandardOutput = true,
            UseShellExecute = false
        };
        MemoryStream opusBytes = new MemoryStream();
        using (Process process = Process.Start(startInfo))
        {
            process.StandardInput.BaseStream.Write(m4.ToArray());
            process.StandardInput.Flush();
            byte[] buffer = new byte[1024];
            int bytes = 0;
            while ((bytes = process.StandardOutput.BaseStream.Read(buffer, 0, buffer.Length)) > 0)
            {
                opusBytes.Write(buffer, 0, bytes);
            }
        }
        Console.WriteLine(m4.Length);
        Console.WriteLine(opusBytes.Length);
        samples.Add(opusBytes.ToArray());
    }
    Console.WriteLine("Recording");
};
waveIn.StartRecording();
Console.ReadLine();
waveIn.StopRecording();
Thread.Sleep(1000);
writer.Close();
foreach(var sample in samples)
{
    //File.WriteAllBytes("temp.opus", sample);
    MemoryStream wavBytes = new MemoryStream();
    ProcessStartInfo startInfo = new ProcessStartInfo
    {
        FileName = "opusdec.exe",
        Arguments = "- -",
        RedirectStandardInput = true,   // Rediriger l'entrée standard
        RedirectStandardOutput = true,                                                          
        UseShellExecute = false
    };
    using (Process process = Process.Start(startInfo))
    {
        process.StandardInput.BaseStream.Write(sample);
        process.StandardInput.Close();
        byte[] buffer = new byte[1024];
        int bytes = 0;
        while ((bytes = process.StandardOutput.BaseStream.Read(buffer, 0, buffer.Length)) > 0)
        {
            wavBytes.Write(buffer, 0, bytes);
        }
    }
    wavBytes.Position = 0;
    waveOut.Init(new RawSourceWaveStream(wavBytes, new WaveFormat(48000,16,2)));
    waveOut.Play();
    //Console.ReadLine();
    while(waveOut.PlaybackState == PlaybackState.Playing)
    { }
}

but opusdec throws Failed to open '-'.

If i unquote //File.WriteAllBytes("temp.opus", sample); and try to decode the file using cmd and opusdec it works fine. If i replace Arguments = "- -", by Arguments = "temp.opus -", it works fine. If i type

    {
        FileName = "opusdec.exe",
        Arguments = "- test.wav",
        RedirectStandardInput = true,   // Rediriger l'entrée standard
        RedirectStandardOutput = true,                                                          
        UseShellExecute = false
    };
    using (Process process = Process.Start(startInfo))
    {
        process.StandardInput.BaseStream.Write(File.ReadAllBytes("temp.opus"));
        process.StandardInput.Close();
        byte[] buffer = new byte[1024];
        int bytes = 0;
        while ((bytes = process.StandardOutput.BaseStream.Read(buffer, 0, buffer.Length)) > 0)
        {
            wavBytes.Write(buffer, 0, bytes);
        }
    }

it also works fine. All of this leads me to thing there is an issue when using stdin and stdout with opusdec.exe. Am i wrong ?