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Writing an AVI file with C#

AviWriter is a c sharp class that can be used to create AVI movies. As it contains unsafe portions it must be compiled with the /unsafe compiler flag.
his class is unsafe code, so it must be compiled with the /unsafe compiler flag.
See Mandelbrot for an example.

AviWriter.cs

using System;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Drawing.Imaging;

public class AviWriter {
  [StructLayout(LayoutKind.Sequential, Pack=1)]
  private struct AVISTREAMINFOW {
    public UInt32    fccType,    fccHandler,   dwFlags,         dwCaps;

    public UInt16    wPriority,  wLanguage;

    public UInt32    dwScale,    dwRate,      
                     dwStart,    dwLength,     dwInitialFrames, dwSuggestedBufferSize,
                     dwQuality,  dwSampleSize, rect_left,       rect_top,        
                     rect_right, rect_bottom,  dwEditCount,     dwFormatChangeCount;

    public UInt16    szName0,  szName1,  szName2,  szName3,  szName4,  szName5,
                     szName6,  szName7,  szName8,  szName9,  szName10, szName11,
                     szName12, szName13, szName14, szName15, szName16, szName17,
                     szName18, szName19, szName20, szName21, szName22, szName23,
                     szName24, szName25, szName26, szName27, szName28, szName29,
                     szName30, szName31, szName32, szName33, szName34, szName35,
                     szName36, szName37, szName38, szName39, szName40, szName41,
                     szName42, szName43, szName44, szName45, szName46, szName47,
                     szName48, szName49, szName50, szName51, szName52, szName53,
                     szName54, szName55, szName56, szName57, szName58, szName59,
                     szName60, szName61, szName62, szName63;
    } 
  // vfw.h
  [StructLayout(LayoutKind.Sequential, Pack=1)]
  private struct AVICOMPRESSOPTIONS {
    public UInt32   fccType;
    public UInt32   fccHandler;
    public UInt32   dwKeyFrameEvery;  // only used with AVICOMRPESSF_KEYFRAMES
    public UInt32   dwQuality;
    public UInt32   dwBytesPerSecond; // only used with AVICOMPRESSF_DATARATE
    public UInt32   dwFlags;
    public IntPtr   lpFormat;
    public UInt32   cbFormat;
    public IntPtr   lpParms;
    public UInt32   cbParms;
    public UInt32   dwInterleaveEvery;
  }

  [StructLayout(LayoutKind.Sequential, Pack=1)]
  public struct BITMAPINFOHEADER {
    public UInt32 biSize;
    public  Int32 biWidth;
    public  Int32 biHeight;
    public  Int16 biPlanes;
    public  Int16 biBitCount;
    public UInt32 biCompression;
    public UInt32 biSizeImage;
    public  Int32 biXPelsPerMeter;
    public  Int32 biYPelsPerMeter;
    public UInt32 biClrUsed;
    public UInt32 biClrImportant;
  }

  public class AviException :  ApplicationException {
    public AviException(string s) : base(s) {}
    public AviException(string s, Int32 hr) : base(s) {
      
      if (hr==AVIERR_BADPARAM) {
        err_msg = "AVIERR_BADPARAM";
      }
      else {
        err_msg = "unknown";
      }
    }
  
    public string ErrMsg() {
      return err_msg;
    }
    private const Int32 AVIERR_BADPARAM = -2147205018;
    private string err_msg;
  }

  public Bitmap Open(string fileName, UInt32 frameRate, int width, int height) {
    frameRate_ = frameRate;
    width_     = (UInt32) width;
    height_    = (UInt32) height;
    bmp_       = new Bitmap(width,height,PixelFormat.Format24bppRgb);
    BitmapData bmpDat = bmp_.LockBits(new Rectangle(0,0,width, height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
    stride_    = (UInt32) bmpDat.Stride;
    bmp_.UnlockBits(bmpDat);
    AVIFileInit();
    int hr = AVIFileOpenW(ref pfile_, fileName, 4097 /* OF_WRITE | OF_CREATE (winbase.h) */, 0);
    if (hr != 0) {
      throw new AviException("error for AVIFileOpenW");
    }

    CreateStream();
    SetOptions();

    return bmp_;
  }

  public void AddFrame() {

    BitmapData bmpDat = bmp_.LockBits(
      new Rectangle(0,0,(int) width_, (int) height_),ImageLockMode.ReadOnly,PixelFormat.Format24bppRgb);

    int hr= AVIStreamWrite(psCompressed_, count_, 1, 
       bmpDat.Scan0, // pointer to data
       (Int32) (stride_  * height_), 
       0, // 16 = AVIIF_KEYFRAMe
       0,
       0); 

     if (hr != 0) {
       throw new AviException("AVIStreamWrite");
     }

     bmp_.UnlockBits(bmpDat);

    count_ ++;
  }

  public void Close() {
    AVIStreamRelease(ps_);
    AVIStreamRelease(psCompressed_);

    AVIFileRelease(pfile_);
    AVIFileExit();
  }

  private void CreateStream() {
    AVISTREAMINFOW strhdr           = new AVISTREAMINFOW();
       strhdr.fccType               = fccType_;
       strhdr.fccHandler            = fccHandler_;
       strhdr.dwFlags               = 0;
       strhdr.dwCaps                = 0;
       strhdr.wPriority             = 0;
       strhdr.wLanguage             = 0;
       strhdr.dwScale               = 1;
       strhdr.dwRate                = frameRate_; // Frames per Second
       strhdr.dwStart               = 0;
       strhdr.dwLength              = 0;
       strhdr.dwInitialFrames       = 0;
       strhdr.dwSuggestedBufferSize = height_ * stride_;
       strhdr.dwQuality             = 0xffffffff; //-1;         // Use default
       strhdr.dwSampleSize          = 0;
       strhdr.rect_top              = 0;
       strhdr.rect_left             = 0;
       strhdr.rect_bottom           = height_;
       strhdr.rect_right            = width_;
       strhdr.dwEditCount           = 0;
       strhdr.dwFormatChangeCount   = 0;
       strhdr.szName0               = 0;
       strhdr.szName1               = 0;

    int hr = AVIFileCreateStream(pfile_, out ps_, ref strhdr);

    if (hr != 0) {
      throw new AviException("AVIFileCreateStream");
    }
  }

  unsafe private void SetOptions() {
      AVICOMPRESSOPTIONS opts = new AVICOMPRESSOPTIONS();
       opts.fccType           = 0; //fccType_;
       opts.fccHandler        = 0;//fccHandler_;
       opts.dwKeyFrameEvery   = 0;
       opts.dwQuality         = 0;  // 0 .. 10000
       opts.dwFlags           = 0;  // AVICOMRPESSF_KEYFRAMES = 4
       opts.dwBytesPerSecond  = 0;
       opts.lpFormat          = 0; //new IntPtr(0);
       opts.cbFormat          = 0;
       opts.lpParms           = 0; //new IntPtr(0);
       opts.cbParms           = 0;
       opts.dwInterleaveEvery = 0;

    AVICOMPRESSOPTIONS* p = &opts;
    AVICOMPRESSOPTIONS** pp = &p;

    IntPtr x       = ps_;
    IntPtr* ptr_ps = &x;

    AVISaveOptions(0,0,1,ptr_ps,pp);



    // TODO: AVISaveOptionsFree(...)
    
    int hr = AVIMakeCompressedStream(out psCompressed_, ps_, ref opts, 0);
    if (hr != 0) {
      throw new AviException("AVIMakeCompressedStream");
    }

    BITMAPINFOHEADER bi    = new BITMAPINFOHEADER();
         bi.biSize         = 40;
         bi.biWidth        = (Int32) width_;
         bi.biHeight       = (Int32) height_;
         bi.biPlanes       = 1;
         bi.biBitCount     = 24;
         bi.biCompression  = 0;  // 0 = BI_RGB
         bi.biSizeImage    = stride_*height_;
         bi.biXPelsPerMeter= 0;
         bi.biYPelsPerMeter= 0;
         bi.biClrUsed      = 0;
         bi.biClrImportant = 0;

    hr = AVIStreamSetFormat(psCompressed_, 0, ref bi, 40);
    if (hr != 0) {
      throw new AviException("AVIStreamSetFormat",hr);
    }
  }

  [DllImport("avifil32.dll")]
  private static extern void AVIFileInit();

  [DllImport("avifil32.dll")]
  private static extern int AVIFileOpenW(ref int ptr_pfile, [MarshalAs(UnmanagedType.LPWStr)]string fileName,int flags, int dummy);

  [DllImport("avifil32.dll")]
  private static extern int AVIFileCreateStream(
    int ptr_pfile, out IntPtr ptr_ptr_avi, ref AVISTREAMINFOW ptr_streaminfo); 

  [DllImport("avifil32.dll")]
  private static extern int AVIMakeCompressedStream(
    out IntPtr ppsCompressed, IntPtr aviStream, ref AVICOMPRESSOPTIONS ao, int dummy);

  [DllImport("avifil32.dll")]
  private static extern int AVIStreamSetFormat(
    IntPtr aviStream, Int32 lPos, ref BITMAPINFOHEADER lpFormat, Int32 cbFormat);

  [DllImport("avifil32.dll")]
  unsafe private static extern int AVISaveOptions(
    int hwnd, UInt32 flags, int nStreams, IntPtr* ptr_ptr_avi, AVICOMPRESSOPTIONS** ao);

  [DllImport("avifil32.dll")]
  private static extern int AVIStreamWrite(
    IntPtr aviStream, Int32 lStart,  Int32 lSamples, IntPtr lpBuffer, 
    Int32   cbBuffer, Int32 dwFlags, Int32 dummy1,   Int32 dummy2);

  [DllImport("avifil32.dll")]
  private static extern int AVIStreamRelease(IntPtr aviStream);

  [DllImport("avifil32.dll")]
  private static extern int AVIFileRelease(int pfile);

  [DllImport("avifil32.dll")]
  private static extern void AVIFileExit();
  
  private int    pfile_        = 0;
  private IntPtr ps_           = new IntPtr(0);
  private IntPtr psCompressed_ = new IntPtr(0);
  private UInt32 frameRate_    = 0;
  private int    count_        = 0;
  private UInt32 width_        = 0;
  private UInt32 stride_       = 0;
  private UInt32 height_       = 0;
  private UInt32 fccType_      = 1935960438;  // vids
  private UInt32 fccHandler_   = 808810089;// IV50
                                 //1145656899;  // CVID
  private Bitmap bmp_;
};
Many thanks to Bernd Rausch who spotted and reported two errors in AviWriter.cs.

Todo

The return value in the call to AVISaveOptions is not checked. That means, the user might press cancel without the program noticing it.