I have .H file, how to open its public methods to .Net library?

Question

I have such .H file (from here)

/*
  FFmpeg simple Encoder
 */


#ifndef __VIDEO_ENCODER_H__
#define __VIDEO_ENCODER_H__

#include "ffmpegInclude.h"
#include <Windows.h>
#include <string>

class VideoEncoder
{
  private:

  // output file name
  std::string     outputFilename;
  // output format.
  AVOutputFormat  *pOutFormat;
  // format context
  AVFormatContext *pFormatContext;
  // video stream context
  AVStream * pVideoStream;
  // audio streams context
  AVStream * pAudioStream;
  // convert context context
  struct SwsContext *pImgConvertCtx;
  // encode buffer and size
  uint8_t * pVideoEncodeBuffer;
  int nSizeVideoEncodeBuffer;

  // audio buffer and size
  uint8_t * pAudioEncodeBuffer;
  int nSizeAudioEncodeBuffer;


  // count of sample
  int audioInputSampleSize;
  // current picture
  AVFrame *pCurrentPicture;

  // audio buffer
  char* audioBuffer;
  int   nAudioBufferSize;
  int   nAudioBufferSizeCurrent;

  public:

  VideoEncoder() 
  {
    pOutFormat = NULL;
    pFormatContext = NULL;
    pVideoStream = NULL;
    pImgConvertCtx = NULL;
    pCurrentPicture = NULL;
    pVideoEncodeBuffer = NULL;
    nSizeVideoEncodeBuffer = 0;
    pAudioEncodeBuffer = NULL;
    nSizeAudioEncodeBuffer = 0;
    nAudioBufferSize = 1024 * 1024 * 4;
    audioBuffer      = new char[nAudioBufferSize];
    nAudioBufferSizeCurrent = 0;
  }

  virtual ~VideoEncoder() 
  {
    Finish();
  }

  // init output file
  bool InitFile(std::string& inputFile, std::string& container);
  // Add video and audio data
  bool AddFrame(AVFrame* frame, const char* soundBuffer, int soundBufferSize);
  // end of output
  bool Finish();

  private: 

  // Add video stream
  AVStream *AddVideoStream(AVFormatContext *pContext, CodecID codec_id);
  // Open Video Stream
  bool OpenVideo(AVFormatContext *oc, AVStream *pStream);
  // Allocate memory
  AVFrame * CreateFFmpegPicture(int pix_fmt, int nWidth, int nHeight);
  // Close video stream
  void CloseVideo(AVFormatContext *pContext, AVStream *pStream);
  // Add audio stream
  AVStream * AddAudioStream(AVFormatContext *pContext, CodecID codec_id);
  // Open audio stream
  bool OpenAudio(AVFormatContext *pContext, AVStream *pStream);
  // close audio stream
  void CloseAudio(AVFormatContext *pContext, AVStream *pStream);
  // Add video frame
  bool AddVideoFrame(AVFrame * frame, AVCodecContext *pVideoCodec);
  // Add audio samples
  bool AddAudioSample(AVFormatContext *pFormatContext, 
    AVStream *pStream, const char* soundBuffer, int soundBufferSize);
  // Free resourses.
  void Free();
  bool NeedConvert();
};

#endif // __VIDEO_ENCODER_H__

I want to encapsulate this "Video Encoder" into some namespace and compile it so that I would be able to acsess that video encoder functions from C# (so I turned that project (link provided above) into dll\library and try to compile it with clr and clr:old... it compiles and dll is acsessible from C# but not its functions/classes... I just do not know what to modify in this class to turn it into acsessible one from .net)

Answer 1

You need to look into P/Invoke, which enables native DLL methods to be called from managed code. It has many gotchas and pitfalls, so be careful, and understand it won't be easy.

Answer 2

I believe what you're looking for is C++/CLI ( http://en.wikipedia.org/wiki/C++/CLI and http://msdn.microsoft.com/en-us/library/xey702bw.aspx ). While I'm no expert myself, I think you might be able to get away with changing the class declaration to

namespace MyNamespace
{
    public ref class VideoEncoder
    {
        // Existing contents of VideoEncoder class
    }
}

(note that you'll also have to edit the matching .cpp file to use the namespace).

If that doesn't work, you should be able to able to write a managed class that wraps the original C++ class.