C# mp3 player

[mp3csharp]

Im trying to make my own C# mp3 playingf library I am using mci, but dont like it - it is bad quality. I dont like using the windows media player or directx stuff either, because they are also bad quality when it works, and you need more stuff installed to run them.

So I look around for open source mp3 playing libraries and the best one out there seems to be mpg123. They have a win32 library call mpglib.dll which plays very well. Unfortunately, its in C, and Im using C#. C# can call functions in C though, so I think it is quite possible. I also have a sample C program that uses the library and it works well.

The C example is at http://www.inet.hr/~zcindori/download/rawmp3_source_dll_version.zip

mpglib.dll is at
http://www.rz.uni-frankfurt.de/~pesch/mpglibdll.zip
or
http://www.lancs.ac.uk/postgrad/ramdhany/code/mp3lib/mpglibdll.zip

Here is my problem and code:

using System;
using System.Runtime.InteropServices;

namespace csmpglibtest
{
/// <summary>
/// Summary description for csMpgLib.
/// </summary>
public class csMpgLib
{
[StructLayout(LayoutKind.Sequential)]
private struct mpstr
{
[MarshalAs(UnmanagedType.ByValArray, SizeConst=40000)]
private char[] c;
}

[DllImport("mpglib.dll", EntryPoint="_InitMP3", CharSet=CharSet.Ansi)]
private static extern bool InitMp3(mpstr mp);

[DllImport("mpglib.dll", EntryPoint="_ExitMP3", CharSet=CharSet.Ansi)]
private static extern void ExitMp3(mpstr mp);

[DllImport("mpglib.dll", EntryPoint="_decodeMp3", CharSet=CharSet.Ansi)]
private static extern int DecodeMp3(mpstr mp, char[] inmemory, int inmemsize, char[] outmemory, int outmemsize, out int done);

public csMpgLib()
{
//
// TODO: Add constructor logic here
//
}

public void Test()
{
mpstr something = new mpstr();
InitMp3(something);
//ExitMp3(something);
}
}
}

the error I get when running is:

An unhandled exception of type System.NullReferenceException occurred in csmpglibtest.exe

Additional information: Object reference not set to an instance of an object.

and the line it yellows is InitMp3(something);


what am I doing wrong? are my functions modified incorrectly? do I need to do something to the class before InitMp3?

I think this is a good project because there are really no good C# mp3 playing libraries out there.

Thanks all,

 

[Damez]

Hmm

Im trying to do this too. Looks like the probem is that the struct needs to be MarshalAs UnmanagedType.Struct ???? Not too sure how to do that!

I tried passing just a char array which works but u need to send it by ref as when the C function returns its empty =/

Im wondering if a more siple C wrapper would be better.

Let me know if u have any more luck and Ill do the same

Ta

D

 

[Damez]

Ive sort of got this doing summot, only it seem to work ok upuntil I get a bogus returncode from the convert function, and then it fails =/

This is wot I have

[DllImport("mpglib.dll", EntryPoint="_InitMP3", CharSet=CharSet.Ansi)]
private static extern bool InitMp3([In,Out]char[] data);

[DllImport("mpglib.dll", EntryPoint="_ExitMP3", CharSet=CharSet.Ansi)]
private static extern void ExitMp3([In,Out] char[] data);

[DllImport("mpglib.dll", EntryPoint="_decodeMP3", CharSet=CharSet.Ansi)]
private static extern int DecodeMp3([In,Out] char[] Data, char[] inmemory, int inmemsize,[In,Out] char[] outmemory, int outmemsize, out int done);

private void button1_Click(object sender, System.EventArgs e)
{
char[] Data = new char[40000];

InitMp3(Data);

FileStream fs = new FileStream("Test.Wav", FileMode.OpenOrCreate);

// Create the writer for data.
BinaryWriter w = new BinaryWriter(fs);

fs = new FileStream("Test.mp3", FileMode.Open, FileAccess.Read);

BinaryReader r = new BinaryReader(fs);

while(true)
{
byte[] trBuffer = r.ReadBytes(16384);
int rLen = trBuffer.Length;

if(rLen <= 0)
{
break;
}

char[] rBuffer = Encoding.ASCII.GetChars(trBuffer);

char[] wBuffer = new char[8192];
int Done = 0;

int ret = DecodeMp3(Data,rBuffer,rLen ,wBuffer,8192 ,out Done);

while(ret == 0)
{
w.Write(wBuffer,0,Done);
ret = DecodeMp3(Data,null,0,wBuffer,8192 ,out Done);
};
};

ExitMp3(Data);
r.Close();
w.Close();
}