1、异步的：

p.StartInfo.RedirectStandardError = true;
p.ErrorDataReceived += new DataReceivedEventHandler(OutputInfo);
p.Start();
p.BeginErrorReadLine();

private void OutputInfo(object sendProcess, DataReceivedEventArgs output){
  if (!String.IsNullOrEmpty(output.Data))
  {
    //处理方法...
  }
}

2、同步的

p.StartInfo.RedirectStandardError = true;
p.Start();
StreamReader sr = ffmpeg.StandardError;
p.WaitForExit();//之后就可以从sr里读了

1、关于enum的定义

enum Fabric
{
  Cotton = 1,
  Silk = 2,
  Wool = 4,
  Rayon = 8,
  Other = 128
}

2、符号名和常数值的互相转换

Fabric fab = Fabric.Cotton;
int fabNum = (int)fab;//转换为常数值。必须使用强制转换。
Fabric fabString = (Fabric)1;//常数值转换成符号名。如果使用ToString()，则是（（Fabric）1）.ToString()，注意必须有括号。
string fabType = fab.ToString();//显示符号名
string fabVal = fab.ToString ("D");//显示常数值

3、获得所有符号名的方法（具体参见Enum类）

public enum MyFamily
{
  YANGZHIPING = 1,
  GUANGUIQIN = 2,
  YANGHAORAN = 4,
  LIWEI = 8,
  GUANGUIZHI = 16,
  LISIWEN = 32,
  LISIHUA = 64,
}
foreach (string s in Enum.GetNames(typeof(MyFamily)))
{
  Console.WriteLine(s);
}

4、将枚举作为位标志来处理

根据下面的两个例子，粗略地说，一方面，设置标志[Flags]或者[FlagsAttribute]，则表明要将符号名列举出来；另一方面，可以通过强制转换，将数字转换为符号名。说不准确。看下面的例子体会吧。注意：

• 例一：

Fabric fab = Fabric.Cotton | Fabric.Rayon | Fabric.Silk;
Console.WriteLine("MyFabric = {0}", fab);//输出：Fabric.Cotton | Fabric.Rayon | Fabric.Silk;

• 例二：

class FlagsAttributeDemo
{
  // Define an Enum without FlagsAttribute.
  enum SingleHue : short
  {
    Black = 0,
    Red = 1,
    Green = 2,
    Blue = 4
  };
  // Define an Enum with FlagsAttribute.
  [FlagsAttribute]
  enum MultiHue : short
  {
    Black = 0,
    Red = 1,
    Green = 2,
    Blue = 4
  };
  static void Main( )
  {
    Console.WriteLine(
    "This example of the FlagsAttribute attribute n" +
    "generates the following output." );
    Console.WriteLine(
    "nAll possible combinations of values of an n" +
    "Enum without FlagsAttribute:n" );
    // Display all possible combinations of values.
    for( int val = 0; val <= 8; val++ )
    Console.WriteLine( "{0,3} – {1}",  val, ( (SingleHue)val ).ToString( ) );
    Console.WriteLine(  "nAll possible combinations of values of an n" + "Enum with FlagsAttribute:n" );
    // Display all possible combinations of values.
    // Also display an invalid value.
    for( int val = 0; val <= 8; val++ )
    Console.WriteLine ( "{0,3} – {1}",  val, ( (MultiHue)val ).ToString( ) );
  }
}
/*
This example of the FlagsAttribute attribute
generates the following output.
All possible combinations of values of an
Enum without FlagsAttribute:
0 – Black
1 – Red
2 – Green
3 – 3
4 – Blue
5 – 5
6 – 6
7 – 7
8 – 8
All possible combinations of values of an
Enum with FlagsAttribute:
0 – Black
1 – Red
2 – Green
3 – Red, Green
4 – Blue
5 – Red, Blue
6 – Green, Blue
7 – Red, Green, Blue
8 – 8
*/

5、枚举作为函数参数。经常和switch结合起来使用。下面举例

public static double GetPrice(Fabric fab)
{
  switch (fab)
  {
    case Fabric.Cotton:
      return (3.55);
    case Fabric.Silk:
      return (5.65);
    case Fabric.Wool:
      return (4.05);
    case Fabric.Rayon:
      return (3.20);
    case Fabric.Other:
      return (2.50);
    default:
      return (0.0);
  }
}

6、上面三点一个完整的例子

//enum的定义
public enum Fabric : short
{
  Cotton = 1,
  Silk = 2,
  Wool = 3,
  Rayon = 8,
  Other = 128
}
//将枚举作为参数传递
public static double GetPrice(Fabric fab)
{
  switch (fab)
  {
    case Fabric.Cotton: return (3.55);
    case Fabric.Silk : return (5.65);
    case Fabric.Wool: return (4.05);
    case Fabric.Rayon: return (3.20);
    case Fabric.Other: return (2.50);
    default: return (0.0);
  }
}
public static void Main()
{
  Fabric fab = Fabric.Cotton;
  int fabNum = (int)fab;
  string fabType = fab.ToString();
  string fabVal = fab.ToString ("D");
  double cost = GetPrice(fab);
  Console.WriteLine("fabNum = {0}nfabType = {1}nfabVal = {2}n", fabNum, fabType, fabVal);
  Console.WriteLine("cost = {0}", cost);
}

7、Enum类的使用

Enum.IsDefinde、Enum.Parse两种方法经常一起使用，来确定一个值或符号是否是一个枚举的成员，然后创建一个实例。Enum.GetName打印出一个成员的值；Enum.GetNames打印出所有成员的值。其中注意**“`typeof“`**的使用。这一点很重要。

public enum MyFamily
{
  YANGZHIPING = 1,
  GUANGUIQIN = 2,
  YANGHAORAN = 4,
  LIWEI = 8,
  GUANGUIZHI = 16,
  LISIWEN = 32,
  LISIHUA = 64,
}
string s = "YANGHAORAN";
if (Enum.IsDefined(typeof(MyFamily), s))
{
  MyFamily f = (MyFamily)Enum.Parse(typeof(MyFamily), s);
  GetMyFamily(f);
  Console.WriteLine("The name is:" + Enum. GetName(typeof(MyFamily), 2));
  string[] sa = Enum.GetNames(typeof(MyFamily));
  foreach (string ss in sa)
  {
    Console.WriteLine(ss);
  }
}