Helyar.net » vlc

libvlc media player in C# (part 2)

George Helyar — Fri, 08 May 2009 15:38:56 +0000

I gave some simplified VLC media player code in part 1 to show how easy it was to do and how most wrapper libraries make a mountain out of a mole hill. In that entry, I briefly touched on using some classes to make it easier and safer to implement actual programs with this.

The first thing to do is write a wrapper for the exceptions, so that they are handled nicely in C#. For a program using the library, exceptions should be completely transparent and should be handled in the normal try/catch blocks without having to do anything like initialise them or check them.

Another thing to do is to move all of the initialisation functions into constructors and all of the release functions into destuctors or use the System.IDisposable interface.

Here is the code listing for the 4 classes used (VlcInstance, VlcMedia, VlcMediaPlayer and VlcException). Note that the first 3 of these are very similar and that the main difference is that the media player class has some extra functions for doing things like playing and pausing the content.

class VlcInstance : IDisposable
{
    internal IntPtr Handle;
 
    public VlcInstance(string[] args)
    {
        VlcException ex = new VlcException();
        Handle = LibVlc.libvlc_new(args.Length, args, ref ex.Ex);
        if (ex.IsRaised) throw ex;
    }
 
    public void Dispose()
    {
        LibVlc.libvlc_release(Handle);
    }
}
 
class VlcMedia : IDisposable
{
    internal IntPtr Handle;
 
    public VlcMedia(VlcInstance instance, string url)
    {
        VlcException ex = new VlcException();
        Handle = LibVlc.libvlc_media_new(instance.Handle, url, ref ex.Ex);
        if (ex.IsRaised) throw ex;
    }
 
    public void Dispose()
    {
        LibVlc.libvlc_media_release(Handle);
    }
}
 
class VlcMediaPlayer : IDisposable
{
    internal IntPtr Handle;
    private IntPtr drawable;
    private bool playing, paused;
 
    public VlcMediaPlayer(VlcMedia media)
    {
        VlcException ex = new VlcException();
        Handle = LibVlc.libvlc_media_player_new_from_media(media.Handle, ref ex.Ex);
        if (ex.IsRaised) throw ex;
    }
 
    public void Dispose()
    {
        LibVlc.libvlc_media_player_release(Handle);
    }
 
    public IntPtr Drawable
    {
        get
        {
            return drawable;
        }
        set
        {
            VlcException ex = new VlcException();
            LibVlc.libvlc_media_player_set_drawable(Handle, value, ref ex.Ex);
            if (ex.IsRaised) throw ex;
            drawable = value;
        }
    }
 
    public bool IsPlaying { get { return playing && !paused; } }
 
    public bool IsPaused { get { return playing && paused; } }
 
    public bool IsStopped { get { return !playing; } }
 
    public void Play()
    {
        VlcException ex = new VlcException();
        LibVlc.libvlc_media_player_play(Handle, ref ex.Ex);
        if (ex.IsRaised) throw ex;
 
        playing = true;
        paused = false;
    }
 
    public void Pause()
    {
        VlcException ex = new VlcException();
        LibVlc.libvlc_media_player_pause(Handle, ref ex.Ex);
        if (ex.IsRaised) throw ex;
 
        if (playing)
            paused ^= true;
    }
 
    public void Stop()
    {
        VlcException ex = new VlcException();
        LibVlc.libvlc_media_player_stop(Handle, ref ex.Ex);
        if (ex.IsRaised) throw ex;
 
        playing = false;
        paused = false;
    }
}
 
class VlcException : Exception
{
    internal libvlc_exception_t Ex;
 
    public VlcException() : base()
    {
        Ex = new libvlc_exception_t();
        LibVlc.libvlc_exception_init(ref Ex);
    }
 
    public bool IsRaised { get { return LibVlc.libvlc_exception_raised(ref Ex) != 0; } }
 
    public override string Message { get { return LibVlc.libvlc_exception_get_message(ref Ex); } }
}

Using these classes is even easier than before, can use proper exception handling (removed for brevity) and cleans up better at the end. In this example, I have added an OpenFileDialog, which is where the file is loaded.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
 
namespace MyLibVLC
{
    public partial class Form1 : Form
    {
        VlcInstance instance;
        VlcMediaPlayer player;
 
        public Form1()
        {
            InitializeComponent();
 
            openFileDialog1.FileName = "";
            openFileDialog1.Filter = "MPEG|*.mpg|AVI|*.avi|All|*.*";
 
            string[] args = new string[] {
                "-I", "dummy", "--ignore-config",
                @"--plugin-path=C:\Program Files (x86)\VideoLAN\VLC\plugins",
                "--vout-filter=deinterlace", "--deinterlace-mode=blend"
            };
 
            instance = new VlcInstance(args);
            player = null;
        }
 
        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
            if(player != null) player.Dispose();
            instance.Dispose();
        }
 
        private void Open_Click(object sender, EventArgs e)
        {
            if (openFileDialog1.ShowDialog() != DialogResult.OK)
                return;
 
            using (VlcMedia media = new VlcMedia(instance, openFileDialog1.FileName))
            {
                if (player != null) player.Dispose();
                player = new VlcMediaPlayer(media);
            }
 
            player.Drawable = panel1.Handle;
        }
 
        private void Play_Click(object sender, EventArgs e)
        {
            player.Play();
        }
 
        private void Pause_Click(object sender, EventArgs e)
        {
            player.Pause();
        }
 
        private void Stop_Click(object sender, EventArgs e)
        {
            player.Stop();
        }
    }
}

Update:

I have just corrected a minor bug (the wrong release function being called on the player handle) and uploaded the full Visual Studio 2005 project. You can download the full project here (or see 1.1.2 version below). It comes with the libvlc.dll and libvlccore.dll for VLC 1.0.1 in the bin\x86\Debug directory so if you have a version other than this, just overwrite those files.

Update for VLC 1.1.2:

You can now download the VLC 1.1.2 compatible version. There were some changes to the way libvlc handles exceptions that needed to be corrected. Other than that, there were a couple of minor function name changes.

Please use these posts as a starting point to use your own code though. These posts are intended to stop people from being reliant on the already existing, large, overcomplicated and quickly outdated libraries. They are not intended to be just another library for people to blindly use without understanding how it works. You can use this to learn how to write your own native interop code on a well designed library then adapt it for your own changes and keep it up to date with whichever version of VLC you want. This also means you never have to use the terrible code on pinvoke.net for other libraries, as you can write your own from the original documentation and it will almost always be better.

Bugfix: VlcException should use Marshal.PtrToStringAnsi not Marshal.PtrToStringAuto

libvlc media player in C# (part 1)

George Helyar — Wed, 06 May 2009 12:44:03 +0000

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:

See part 2 for more.