[C# Express 2008] Problem on executing program with parameter directory japanese

Hello to everyone, first of all sorry for my bad english, I will try to explain my problem.
I am trying to make a simple program in c# that using the sofware FFMpeg: http://www.videohelp.com/tools/ffmpeg
can extract some information from the output created from it.
So I just created a ProcessStartInfo(pathofffmpeg , parameters)
where parameters it's a string just like that:
" -i pathoffileandfile.avi"
All work fine if the directory or the file have just normal ascii code, but as per example I have to extract information from that file:
E:\春の朝は寒い\Somefile.avi
then I just get from ffmpeg an error because can't get the file E:\??????\Somefile.avi and as you can see the ?????? substitute the correct character of the path.
So I did another try, I went to my XP pc and change Locale to japanese, and try to execute the same command inside a BAT file or just from command prompt and that work !
ffmpeg parameters input expected to be codified into UTF-8 format and actually I tried it too as follow:

string Params = string.Format("-i \"{0}\"", @input.Path);
Encoding srcEncodingFormat = Encoding.GetEncoding("UTF-16LE"); // standard for string ??
Encoding dstEncodingFormat = Encoding.UTF8;
byte[] originalByteString = srcEncodingFormat.GetBytes(Params);
byte[] convertedByteString = Encoding.Convert(srcEncodingFormat,
dstEncodingFormat, originalByteString);
string finalString = dstEncodingFormat.GetString(convertedByteString);

string output = RunProcess(finalString);

where RunProcess it's that function

private string RunProcess(string Parameters)
{
//create a process info
ProcessStartInfo oInfo = new ProcessStartInfo(this.FFmpegPath, Parameters);
oInfo.UseShellExecute = false;
oInfo.CreateNoWindow = true;
oInfo.RedirectStandardOutput = true;
oInfo.RedirectStandardError = true;
//Create the output
string output = null;
//try the process
try
{
//run the process
Process proc = System.Diagnostics.Process.Start(oInfo);
//now put it in a string
output = proc.StandardError.ReadToEnd();
//Wait for exit
proc.WaitForExit();
//Release resources
proc.Close();
}
catch (Exception)
{
output = string.Empty;
}
return output;
}

Results, not working :( Any suggestion about what to do ?????