var envar = Environment.GetEnvironmentVariable("PATH"); // Just the Path, no Exe
int found = 0;


// Check All Environment Variables Paths for ffmpeg.exe
//
foreach (var envarPath in envar.Split(';'))
{
    // Path + Exe
    var exePath = System.IO.Path.Combine(envarPath, "ffmpeg.exe");

    // Check
    if (File.Exists(exePath))
    {
        found = 1;
    }
}


// Display Message if FFmpeg exists
//
if (found == 1)
{
    MessageBox.Show("FFmpeg exists.");
}
else if (found == 0)
{
    MessageBox.Show("Cannot locate FFmpeg.");
}