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• FFmpeg sws_scale crash at certain resolution

  23 mai 2016, par Tamás Szobonya

  I’m having a weird issue with sws_scale. The problem is, that at certain resolutions i got an Access violation reading location exception. Resolutions like 1920x1080, 1600x900 works, but 1280x720 doesn’t ? This happens in a c++ cli code which is called from c#. Every project is x64 build (no Any CPU) on a Win7 x64.

  c++ cli code :

  void FFmpegWrapper::Codec::E(int width, int height, IntPtr dataIn, [Out] IntPtr %dataOut)
  
  {
  
      int ret;
  
      AVFrame *f, *fIn, *fOut;
  
      f = av_frame_alloc();
  
      fIn = av_frame_alloc();
  
      fOut = av_frame_alloc();
  
  
  
      fIn->format = AV_PIX_FMT_RGB24;
  
      fIn->width = width;
  
      fIn->height = height;
  
      ret = av_image_alloc(fIn->data, fIn->linesize, width, height, AV_PIX_FMT_RGB24, 32);
  
  
  
      f->format = AV_PIX_FMT_YUV420P;
  
      f->width = width;
  
      f->height = height;
  
      ret = av_image_alloc(f->data, f->linesize, width, height, AV_PIX_FMT_YUV420P, 32);
  
  
  
      fOut->format = AV_PIX_FMT_RGB24;
  
      fOut->width = width;
  
      fOut->height = height;
  
      ret = av_image_alloc(fOut->data, fOut->linesize, width, height, AV_PIX_FMT_RGB24, 32);
  
  
  
  
  
      uint8_t *data = (uint8_t*)dataIn.ToPointer();
  
      fIn->data[0] = data;
  
  
  
      //with or without struct no difference
  
      /*struct */SwsContext *convertCtx = sws_getContext(width, height, AV_PIX_FMT_RGB24, width, height, AV_PIX_FMT_YUV420P, 0, NULL, NULL, NULL);
  
  
  
      // CRASH here
  
      sws_scale(convertCtx, fIn->data, fIn->linesize, 0, height, f->data, f->linesize);
  
  
  
      convertCtx = sws_getContext(width, height, AV_PIX_FMT_YUV420P, width, height, AV_PIX_FMT_RGB24, 0, NULL, NULL, NULL);
  
  
  
      sws_scale(convertCtx, f->data, f->linesize, 0, height, fOut->data, fOut->linesize);
  
  
  
      dataOut = (IntPtr)fIn->data[0];
  
  
  
  }

  And its called from c# like this :

  FFmpegWrapper.Codec test = new FFmpegWrapper.Codec();
  
  
  
  Bitmap image = new Bitmap(w, h, PixelFormat.Format24bppRgb);
  
  
  
  // Get a screenshot from the desktop
  
  Screen.Capture(w, h, image, PixelFormat.Format24bppRgb);
  
  
  
  Rectangle rec = new Rectangle(0, 0, image.Width, image.Height);
  
  BitmapData bitmapData = image.LockBits(rec, ImageLockMode.ReadWrite, image.PixelFormat);
  
  
  
  IntPtr ptr = bitmapData.Scan0;
  
  
  
  IntPtr testptr1;
  
  
  
  test.E(w, h, ptr, out testptr1);
  
  
  
  // We never reach this with 1280x720 resolution
  
  Bitmap bmp = new Bitmap(w, h, w * 3, PixelFormat.Format24bppRgb, testptr1);
  
  
  
  bmp.Save(@"H:\sajt1.bmp", ImageFormat.Bmp);

  What i don’t understand is, how can it work with certain resolutions and crash with others ?
  Using 20160512-git-cd244fa-win64 version of ffmpeg.

  Edit :
  It seems, that changing AV_PIX_FMT_RGB24 to AV_PIX_FMT_BGR24 fixes it, but I’m not sure why. I know that .Net stores the pixels in bgr, but why does wrong format crashes it ? And only at some resolutions ?

• Taking a high resolution picture with FFMPEG and Webcam

  13 mai 2016, par user2088176

  I have a Microsoft LifeCam VX-3000 and I want to capture a single image from this video source.

  I have tried DirectShow :

  ffmpeg -f dshow -video_size 1280x960 -i video="Microsoft LifeCam VX-3000" -vframes 1 file.jpg
  
  
  
  [dshow @ 01D69340] Could not set video options

  and
  Microsoft WDM Image Capture :

  ffmpeg -f vfwcap -video_size 1280x960 -i video="Microsoft LifeCam VX-3000" -vframes 1 file.jpg
  
  
  
  [vfwcap @ 01D79340] Could not set Video Format.

  If I lower the video size to 640x480, it works, but every sites tells me that 640x480 is the maximum video resolution, but the still picture maximum resolution is 1280x960. Like here

  I would like to capture the image at the highest resolution possible. Is there a way to do it with FFMPEG ? What command-line options should I give it ?

  Thank you very much.

• How to get the highest resolution, dividable by 2 that contains the video without black borders after rotation ?

  22 avril 2016, par Vitalis Hommel

  I rotate a video. Then my goal is to get the biggest resolution, dividable by 2 that contains the video without black borders.

  

  to

  

  My approach.

  ffmpeg -ss 6 -i "t.MP4" -ss 0 -t 5 -vf "rotate='8*PI/180:ow=hypot(iw,ih):oh=ow', scale='1920:1920', crop='1920:1080:0:420'" -c:v libx264 -crf 28 -acodec copy "t2.MP4"

  But that does not meet the criteria. Which command do I need ?