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• FFmpeg (sharpFFmpeg) decoding - Protected memory error

  25 août 2011, par mazharenko.a

  I'm trying to use C# binding of FFmpeg library calling SharpFFmpeg to decode H264 video stream that I receive by RTP. I think I correctly decapsulate NALUs from RTP-packets, but I can't decode complete frames. Function avcodec_decode_video calling throws an AccessViolationException (Attempted to read or write protected memory).
  Here are some code lines :

      //buf is a byte array containing encoded frame
  
      int success;
  
      FFmpeg.avcodec_init();
  
      FFmpeg.avcodec_register_all();
  
      IntPtr codec = FFmpeg.avcodec_find_decoder(FFmpeg.CodecID.CODEC_ID_H264);
  
      IntPtr codecCont = FFmpeg.avcodec_alloc_context(); //AVCodecContext
  
      FFmpeg.avcodec_open(codecCont, codec);
  
      IntPtr frame = FFmpeg.avcodec_alloc_frame();  //AVFrame
  
      FFmpeg.avcodec_decode_video(codecCont, frame, ref success, (IntPtr)buf[0], buf.Length); //exception

  Function has been imported as follows :

      [DllImport("avcodec.dll", CallingConvention = CallingConvention.Cdecl), SuppressUnmanagedCodeSecurity]
  
      public unsafe static extern int avcodec_decode_video(IntPtr pAVCodecContext, IntPtr pAVFrame, ref int got_picture_ptr, IntPtr buf, int buf_size);

  Unfortunately, I don't know what do I have to do with the codecCont. Somebody wrote that it is needed to fill this structure by AVCDCR using session description received by RTSP. But I don't know which field(s) store this record.
  I'll be glad for any help.
  P.S. Excuse me for my English

• How to capture a layered window with transparency background properly ? (using BitBlt)

  25 octobre 2016, par Mitra M

  I want to capture a WPF window (WPF layered window) with transparency background.

  To do that I tried FFmpeg, But :

  1 - If I set AllowTransparency (this is a property of WPF window) to false ,I can capture the window by gdigrab (this is an ffmpeg device), but output has black background.(I don’t want black background)

  2 - If I set AllowTransparency to true then gdigrab won’t work. (get black frame only)

  I have read David’s nice article, he has said :

  if you use BitBlt to do this, you could “or in” the CAPTUREBLT flag if
  you wanted to capture windows that are layered

  The gdigrab uses BitBlt, this is gdigrab.c code snippet :

  /* Blit screen grab */
  
      if (!BitBlt(dest_hdc, 0, 0,
  
                  clip_rect.right - clip_rect.left,
  
                  clip_rect.bottom - clip_rect.top,
  
                  source_hdc,
  
                  clip_rect.left, clip_rect.top, SRCCOPY | CAPTUREBLT)) {
  
          WIN32_API_ERROR("Failed to capture image");
  
          return AVERROR(EIO);
  
      }

  You can see the flags . (SRCCOPY | CAPTUREBLT).

  Please tell me :

  1- Why the gdigrab can not capture a WPF window properly ?

  2 - What changes in this code should be done to do this ?

  (Sorry for my English, I used translate.google)

  Thanks

• Windows : can't generate libx264.dll because MinGW : no working c compiler found

  27 avril 2015, par Sandie C

  It’s my first post in a forum ever (and in english...) Any suggestion is welcomed.

  So let’s started !

  My global goal is to recorder/transcoding and display an IP Camera stream from a .bat whitch calling vlc. (I tried before doing it with VLC interface and it’s going well. I don’t understand why the encoder is missing using that way)

  I want an asf container containing h264 and aac.

  ---

  .bat :

  cd C :\Program Files (x86)\VideoLAN\VLC

  vlc rtsp ://root:root@ip_adresse/media.amp —sout "#transcode vcodec=x264, vb=112 , acodec==aac, fps=25:duplicatedst=display,dst=standardaccess=file,mux = asf,dst=flux.asf" -v

  ---

  when I first execute this, VLC told me that H264 encoder was not found, so I decided to compile x264.

  I used this link

  http://www.ayobamiadewole.com/Blog/How-to-build-x264-or-libx264.dll-in-Windows

  I succeed to make the .exe but and when I got to

  ./configure —disable-cli —enable-shared —extra-ldflags=-Wl,—output-def=libx264.def

  minGW shell indicates : no working c compiler found

  I find some answer, but i didn’t found the good one.

  Does anyone have an idea of what i’m doing wrong ?

  Is it possible that my gcc (4.6) is not the good one ? What should I do ?

  Need another advice :
  When I would have this libx264.ddl where should I put it to make my script working ?

  Early thanks for your answers.