libvlc media player in C# (part 1)

原文 http://www.helyar.net/2009/libvlc-media-player-in-c/

There seems to be a massive misconception about using VLC inside an application and many, many large wrapper libraries have been written. These are often harder to use than libvlc itself, buggy or just downright don’t work (at least not in what will be “the latest” version of VLC at the time you want to write anything).

Using the libvlc documentation directly and the libvlc example I wrote a simple wrapper class that performs the basics needed to play, pause and stop media. Because it is libvlc, things like resizing the video, toggling full screen by double clicking the video output or streaming media from a source device or network are handled automatically.

This code was all written and tested with VLC 0.98a but because it is taken from the documentation and example, it should work for all versions 0.9x and later with only minor changes. Because it is so simple, these changes should be easy to make. Most of the time, these changes will just be slight function name changes and no new re-structuring is needed.

The first thing to note is that there is no version of libvlc for Windows x64. All developers should set their CPU type to x86, even if they have a 32bit machine. If you set it to “Any CPU” then 64bit users will not be able to load libvlc.dll and will crash out. If you are compiling from the command line, this should look something like csc /platform:x86 foobar.cs

The second thing to note, which trips up a lot of users, is that you must specify VLC’s plugin directory. This may make distribution a nightmare, as the plugin directory is a large directory full of DLLs. It may be possible to narrow down these DLLs to just the ones your application actually needs but I don’t know if videolan have any advice about or licensing for redistribution of these.

libvlc is made up of several modules. For the sake of simplicity in this example, I will use 1 static class to contain every exported C function and split them up visually by module with #region.

The nicest thing about VLC, as far as interop with C# goes, is that all memory management is handled internally by libvlc and functions are provided for doing anything that you would need to do to their members. This means that using an IntPtr is suitable for almost everything. You just need to make sure that you pass the correct IntPtr into each function but another layer of C# encapsulating this would easily be able to make sure of that, as discussed in part 2. The only structure that you need to define is an exception, which is very simple. You then simply always pass in references to these structs with ref ex.

The code listing for the wrapper class is as follows:

using System;
using System.Runtime.InteropServices;
 
namespace MyLibVLC
{
  // http://www.videolan.org/developers/vlc/doc/doxygen/html/group__libvlc.html
 
  [StructLayout(LayoutKind.Sequential, Pack = 1)]
  struct libvlc_exception_t
  {
    public int b_raised;
    public int i_code;
    [MarshalAs(UnmanagedType.LPStr)]
    public string psz_message;
  }
 
  static class LibVlc
  {
    #region core
    [DllImport("libvlc")]
    public static extern IntPtr libvlc_new(int argc, [MarshalAs(UnmanagedType.LPArray,
      ArraySubType = UnmanagedType.LPStr)] string[] argv, ref libvlc_exception_t ex);
 
    [DllImport("libvlc")]
    public static extern void libvlc_release(IntPtr instance);
    #endregion
 
    #region media
    [DllImport("libvlc")]
    public static extern IntPtr libvlc_media_new(IntPtr p_instance,
      [MarshalAs(UnmanagedType.LPStr)] string psz_mrl, ref libvlc_exception_t p_e);
 
    [DllImport("libvlc")]
    public static extern void libvlc_media_release(IntPtr p_meta_desc);
    #endregion
 
    #region media player
    [DllImport("libvlc")]
    public static extern IntPtr libvlc_media_player_new_from_media(IntPtr media,
      ref libvlc_exception_t ex);
 
    [DllImport("libvlc")]
    public static extern void libvlc_media_player_release(IntPtr player);
 
    [DllImport("libvlc")]
    public static extern void libvlc_media_player_set_drawable(IntPtr player, IntPtr drawable,
      ref libvlc_exception_t p_e);
 
    [DllImport("libvlc")]
    public static extern void libvlc_media_player_play(IntPtr player, ref libvlc_exception_t ex);
 
    [DllImport("libvlc")]
    public static extern void libvlc_media_player_pause(IntPtr player, ref libvlc_exception_t ex);
 
    [DllImport("libvlc")]
    public static extern void libvlc_media_player_stop(IntPtr player, ref libvlc_exception_t ex);
    #endregion
 
    #region exception
    [DllImport("libvlc")]
    public static extern void libvlc_exception_init(ref libvlc_exception_t p_exception);
 
    [DllImport("libvlc")]
    public static extern int libvlc_exception_raised(ref libvlc_exception_t p_exception);
 
    [DllImport("libvlc")]
    public static extern string libvlc_exception_get_message(ref libvlc_exception_t p_exception);
    #endregion
  }
}

For a sample application to use this simple wrapper, I just created a new Windows form and added a play button, stop button and a panel for viewing the video. In this example, the stop button also cleans everything up so you should make sure to press it before closing the form.

At one point during this code, libvlc can optionally be given a HWND to draw to. If you don’t give it one, it pops up a new player. However, people seem to be confused over how simple this is to do in C# and have been making large amounts of interop calls to the Win32 API to get handles. This is not necessary, as System.Windows.Forms.Control.Handle allows you go get the window handle (HWND) to any component that inherits from the Control class. This includes the Form class and the Panel class (and even the Button class) so all you actually need to pass it is this.Handle (for the handle to the form itself) or panel.Handle (for a Panel called panel). If you want it to start fullscreen, add the command line argument “-f” rather than using the Win32 function GetDesktopWindow().

Because I will be using this to display PAL video, which is interlaced at 576i, I have added some deinterlacing options to the command line. These are --vout-filter=deinterlace and --deinterlace-mode=blend.

Without further ado, here is the code listing for the partial windows form class:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
 
using System.Runtime.InteropServices;
 
namespace MyLibVLC
{
  public partial class Form1 : Form
  {
    IntPtr instance, player;
 
    public Form1()
    {
      InitializeComponent();
    }
 
    private void Play_Click(object sender, EventArgs e)
    {
      libvlc_exception_t ex = new libvlc_exception_t();
      LibVlc.libvlc_exception_init(ref ex);
 
      string[] args = new string[] {
        "-I", "dummy", "--ignore-config",
        @"--plugin-path=C:\Program Files (x86)\VideoLAN\VLC\plugins",
        "--vout-filter=deinterlace", "--deinterlace-mode=blend"
      };
 
      instance = LibVlc.libvlc_new(args.Length, args, ref ex);
      Raise(ref ex);
 
      IntPtr media = LibVlc.libvlc_media_new(instance, @"C:\foobar.mpg", ref ex);
      Raise(ref ex);
 
      player = LibVlc.libvlc_media_player_new_from_media(media, ref ex);
      Raise(ref ex);
 
      LibVlc.libvlc_media_release(media);
 
      // panel1 may be any component including a System.Windows.Forms.Form but
      // this example uses a System.Windows.Forms.Panel
      LibVlc.libvlc_media_player_set_drawable(player, panel1.Handle, ref ex);
      Raise(ref ex);
 
      LibVlc.libvlc_media_player_play(player, ref ex);
      Raise(ref ex);
    }
 
    private void Stop_Click(object sender, EventArgs e)
    {
      libvlc_exception_t ex = new libvlc_exception_t();
      LibVlc.libvlc_exception_init(ref ex);
 
      LibVlc.libvlc_media_player_stop(player, ref ex);
      Raise(ref ex);
 
      LibVlc.libvlc_media_player_release(player);
      LibVlc.libvlc_release(instance);
    }
 
    static void Raise(ref libvlc_exception_t ex)
    {
      if (LibVlc.libvlc_exception_raised(ref ex) != 0)
        MessageBox.Show(LibVlc.libvlc_exception_get_message(ref ex));
    }
  }
}

Note that this section of code is deprecated and the code from part 2 should be used instead.

Adding a pause button is similar to the stop button but without the cleanup.

Here is an example slightly further on down the line but using the same code: