ffmpeg writing the output of the command to a text file doesn't work with C#

Question

I am using ffmpeg commands with C# processes. I used a command to change the audio of a video and it was working but I also wanted to write the output to a text file. The new command works from cmd but apparently, it does not work while using a C# process. The command that does not work with the Process is:

ffmpeg -i videoPath -i audioPath -c:v copy -map 0:v:0 -map 1:a:0 -shortest newVideoPath > textFilePath 2>&1

And the working command is the same without the last part:

ffmpeg -i videoPath -i audioPath -c:v copy -map 0:v:0 -map 1:a:0 -shortest newVideoPath

Here is the C# code:

 Process proc = new Process();
 proc.StartInfo.FileName = ffmpegPath;
 proc.StartInfo.RedirectStandardError = true;
 proc.StartInfo.RedirectStandardOutput = true;
 proc.StartInfo.UseShellExecute = false;
 proc.StartInfo.CreateNoWindow = true;
 proc.StartInfo.Arguments = "-i " + videoPath + " -i " + newAudioPath + " -c:v copy" + " -map" + " 0:v:0 " + "-map 1:a:0 " + "-shortest " + newVideoPath + " > " + @"F:\Videos\log.txt"+ " 2>&1";
 proc.EnableRaisingEvents = true;
 proc.Exited += UpdateVideoSource;
 proc.Start();

I checked the arguments over and over again, and looked for missing spaces but nothing worked. What can be the problem?

Answer 1

ffmpeg has the option -report :

Dump full command line and log output to a file named program-YYYYMMDD-HHMMSS.log in the current directory.

By default, the file generated follow the parttern program-YYYYMMDD-HHMMSS.log. To specify a file, you can set the environnement variable variable FFREPORT :

FFREPORT=file=ffreport.log:level=verbose

In C#, you can start a process with a specific environnement variables by ProcessStartInfo.EnvironmentVariables :

Process proc = new Process();
proc.StartInfo.FileName = ffmpegPath;
proc.StartInfo.RedirectStandardError = false; // Don't redirect the output
proc.StartInfo.RedirectStandardOutput = false;
proc.StartInfo.UseShellExecute = false;
proc.StartInfo.CreateNoWindow = true;
//Add the argument -report
proc.StartInfo.Arguments = "-i " + videoPath + " -i " + newAudioPath + " -c:v copy" + " -map" + " 0:v:0 " + "-map 1:a:0 " + "-shortest " + newVideoPath + " -report";
//Set the output file and the log level
proc.StartInfo.EnvironmentVariables["FFREPORT"] = "file=ffreport.log:level=verbose";
proc.EnableRaisingEvents = true;
proc.Exited += UpdateVideoSource;
proc.Start();

I haven't tested, but this is good start.