C# ffmpeg how to read input from stream

Question

I'm trying to read use the pipe feature of ffmpeg to not have to write files in the disk.

my inputs implementations are:

public FFMPEG input(string path)
{
    parameters.Add($"-i {path}");
    return this;
}
public FFMPEG input(byte[] file)
{
    parameters.Add("-i pipe:.mp4");
    files.Add(file);
    return this;
}

my output implementation is:

public FFMPEG output(string format)
{
    _output = $"-f {format} -";
    return this;
}

my run implementation is:

public byte[] run()
{
    if (_output == "")
    {
        throw new Exception("missing output format");
    }

    var process = new Process()
    {
        StartInfo =
        {
            FileName = @"ffmpeg.exe",
            Arguments = String.Join(" ", parameters) + " " + _output,
            RedirectStandardOutput = true,
            RedirectStandardInput = true,
            UseShellExecute = false,
        }
    };

    process.Start();

    foreach (var item in files)
    {
        process.StandardInput.BaseStream.Write(item);
    }

    byte[] result;
    using(var memstream = new MemoryStream())
    {
        process.StandardOutput.BaseStream.CopyTo(memstream);
        result = memstream.ToArray();
    }
    process.WaitForExit();

    return result;
}

which works perfectly if I use a file as input:

var result = new FFMPEG()
.input("./assets/video.mp4")
.output("avi")
.run();

but when I try to use bytes input:

var result = new FFMPEG()
    .input(File.ReadAllBytes("./assets/video.mp4"))
    .output("avi")
    .run();

I get the following error:

[mov,mp4,m4a,3gp,3g2,mj2 @ 00000137385a10c0] stream 1, offset 0x30: partial file
Error demuxing input file 0: Invalid data found when processing input
pipe:.mp4: Invalid data found when processing input
Cannot determine format of input stream 0:0 after EOF
Error marking filters as finished