Why process output reader returns null data? When same code in other process works correct

I try to get output from ffmpeg process but cant get output. In another processes and commands it works correctly but output returns immideately when start!

        using (var process = new Process())
        {
            process.StartInfo = new ProcessStartInfo()
            {
                FileName = LinkHelper.IPFS_PATH,
                Arguments = cmd,
                UseShellExecute = false,
                CreateNoWindow = true,
                RedirectStandardOutput = true
            };

            process.ErrorDataReceived += FfmpegErrorRecieved;
            process.Start();

            using (StreamReader reader = process.StandardOutput)
            {
                string output = await reader.ReadToEndAsync();
                Console.WriteLine(output);
            }               
            process.WaitForExit();
        }

Before output handle!

Update: As szatmary said ffmpeg use output error instead standard output, so when you initialize process.StandartInfo don't forget initialize property "RedirectStandardError" to TRUE!

Here is correct code:

private async Task DetectFFmpegCamerasAsync()
    {
        var cmd = "-list_devices true -f dshow -i dummy";
        using (var process = new Process())
        {
            process.StartInfo = new ProcessStartInfo()
            {
                FileName = LinkHelper.FFMPEG_PATH,
                Arguments = cmd,
                UseShellExecute = false,
                CreateNoWindow = true,
                RedirectStandardError = true
            };

            process.Start();

            using (StreamReader reader = process.StandardError)
            {
                string output = await reader.ReadToEndAsync();
                Console.WriteLine($"Camera detection output: \n {output}");
            }               
            process.WaitForExit();
        }
    }