How to get the output of a System.Diagnostics.Process?

Question

I run ffmpeg like this:

System.Diagnostics.Process p = new System.Diagnostics.Process();
p.StartInfo = new System.Diagnostics.ProcessStartInfo(ffmpegPath, myParams);
p.Start();
p.WaitForExit();

... but the problem is that the console with ffmpeg pops up and disappears right away, so I can't get any feedback. I don't even know if the process ran correctly.

So how can I either:

• Tell the console to stay opened

• Retrieve in the C# what the console displayed

Answer 1

What you need to do is capture the Standard Output stream:

p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.UseShellExecute = false;
// instead of p.WaitForExit(), do
string q = "";
while ( ! p.HasExited ) {
    q += p.StandardOutput.ReadToEnd();
}

You may also need to do something similar with StandardError. You can then do what you wish with q.

It is a bit finicky, as I discovered in one of my questions

As Jon Skeet has pointed out, it is not smart performance-wise to use string concatenation like this; you should instead use a StringBuilder:

p.StartInfo.RedirectStandardOutput = true;
p.StartInfo.UseShellExecute = false;
// instead of p.WaitForExit(), do
StringBuilder q = new StringBuilder();
while ( ! p.HasExited ) {
    q.Append(p.StandardOutput.ReadToEnd());
}
string r = q.ToString();

Answer 2

I know this question is old, but I'll add to it anyway.

If all you wish to do is display the output of a command line process, and you're spawning the process from a console window, you need only redirect the standard input (yes, I know it sounds wrong, but it works).

So:

System.Diagnostics.Process p = new System.Diagnostics.Process();
p.StartInfo = new System.Diagnostics.ProcessStartInfo(ffmpegPath, myParams);
p.UseShellExecute = false;
p.RedirectStandardInput = true;
p.Start();
p.WaitForExit();

Would do just fine.