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• Greed is Good ; Greed Works

  25 novembre 2010, par Multimedia Mike — VP8

  Greed, for lack of a better word, is good ; Greed works. Well, most of the time. Maybe.

  Picking Prediction Modes
  VP8 uses one of 4 prediction modes to predict a 16x16 luma block or 8x8 chroma block before processing it (for luma, a block can also be broken into 16 4x4 blocks for individual prediction using even more modes).

  So, how to pick the best predictor mode ? I had no idea when I started writing my VP8 encoder. I did not read any literature on the matter ; I just sat down and thought of a brute-force approach. According to the comments in my code :

  // naive, greedy algorithm :
  //   residual = source - predictor
  //   mean = mean(residual)
  //   residual -= mean
  //   find the max diff between the mean and the residual
  // the thinking is that, post-prediction, the best block will
  // be comprised of similar samples
  

  After removing the predictor from the macroblock, individual 4x4 subblocks are put through a forward DCT and quantized. Optimal compression in this scenario results when all samples are the same since only the DC coefficient will be non-zero. Failing that, when the input samples are at least similar to each other, few of the AC coefficients will be non-zero, which helps compression. When the samples are all over the scale, there aren’t a whole lot of non-zero coefficients unless you crank up the quantizer, which results in poor quality in the reconstructed subblocks.

  Thus, my goal was to pick a prediction mode that, when applied to the input block, resulted in a residual in which each element would feature the least deviation from the mean of the residual (relative to other prediction choices).

  Greedy Approach
  I realized that this algorithm falls into the broad general category of "greedy" algorithms— one that makes locally optimal decisions at each stage. There are most likely smarter algorithms. But this one was good enough for making an encoder that just barely works.

  Compression Results
  I checked the total file compression size on my usual 640x360 Big Buck Bunny logo image while forcing prediction modes vs. using my greedy prediction picking algorithm. In this very simple test, DC-only actually resulted in slightly better compression than the greedy algorithm (which says nothing about overall quality).

  prediction mode	quantizer index = 0 (minimum)	quantizer index = 10
  greedy	286260	98028
  DC	280593	95378
  vertical	297206	105316
  horizontal	295357	104185
  TrueMotion	311660	113480

  As another data point, in both quantizer cases, my greedy algorithm selected a healthy mix of prediction modes :

  • quantizer index 0 : DC = 521, VERT = 151, HORIZ = 183, TM = 65
  • quantizer index 10 : DC = 486, VERT = 167, HORIZ = 190, TM = 77

  Size vs. Quality
  Again, note that this ad-hoc test only measures one property (a highly objective one)— compression size. It did not account for quality which is a far more controversial topic that I have yet to wade into.

• Converting uint8_t data to AVFrame with FFmpeg

  30 octobre 2017, par J.Lefebvre

  I am currently working in C++ with the Autodesk 3DStudio Max 2014 SDK (toolset 100) and the Ffmpeg library in Visual Studio 2015 and trying to convert a DIB (Device Independent Bitmap) to uint8_t pointer array and then convert these data to an AVFrame.

  I don’t have any errors, but my video is still black and without meta data.
  (no time display, etc)

  I made approximatively the same with a Visual Studio Console application to convert jpeg image sequence from disk and this is working fine.
  (The only difference is that instead of converting jpeg to AVFrame with the Ffmpeg library, I try to convert raw data to an AVFrame.)

  So I think the problem could be either on the DIB conversion to the uint8_t data or the uint8_t data to the AVFrame.
  (The second is more plausible, because I used the SFML library to display a window with my rgb uint8_t* data for debuging and it is working fine.)

  I first initialize the ffmpeg library :

  This function is called once at the beginning.

  int Converter::Initialize(AVCodecID codec_id, int width, int height, int fps, const char *filename)
  
  {
  
      avcodec_register_all();
  
      av_register_all();
  
  
  
      AVCodec *codec;
  
      inputFrame = NULL;
  
      codecContext = NULL;
  
      pkt = NULL;
  
      file = NULL;
  
      outputFilename = new char[strlen(filename)]();
  
      *outputFilename = '\0';
  
      strcpy(outputFilename, filename);
  
  
  
      int ret;
  
  
  
      //Initializing AVCodecContext and getting PixelFormat supported by encoder
  
      codec = avcodec_find_encoder(codec_id);
  
      if (!codec)
  
          return 1;
  
  
  
      AVPixelFormat pixFormat = codec->pix_fmts[0];
  
      codecContext = avcodec_alloc_context3(codec);
  
      if (!codecContext)
  
          return 1;
  
  
  
      codecContext->bit_rate = 400000;
  
      codecContext->width = width;
  
      codecContext->height = height;
  
      codecContext->time_base.num = 1;
  
      codecContext->time_base.den = fps;
  
      codecContext->gop_size = 10;
  
      codecContext->max_b_frames = 1;
  
      codecContext->pix_fmt = pixFormat;
  
  
  
      if (codec_id == AV_CODEC_ID_H264)
  
          av_opt_set(codecContext->priv_data, "preset", "slow", 0);
  
  
  
      //Actually opening the encoder
  
      if (avcodec_open2(codecContext, codec, NULL) < 0)
  
          return 1;
  
  
  
      file = fopen(outputFilename, "wb");
  
      if (!file)
  
          return 1;
  
  
  
      inputFrame = av_frame_alloc();
  
      inputFrame->format = codecContext->pix_fmt;
  
      inputFrame->width = codecContext->width;
  
      inputFrame->height = codecContext->height;
  
  
  
      ret = av_image_alloc(inputFrame->data, inputFrame->linesize, codecContext->width, codecContext->height, codecContext->pix_fmt, 32);
  
  
  
      if (ret < 0)
  
          return 1;
  
  
  
      return 0;
  
  }

  Then for each frame, I get the DIB and convert to a uint8_t* it with this function :

  uint8_t* Util::ToUint8_t(RGBQUAD *data, int width, int height)
  
  {
  
      uint8_t* buf = (uint8_t*)data;
  
  
  
      int imageSize = width * height;
  
      size_t rgbquad_size = sizeof(RGBQUAD);
  
      size_t total_bytes = imageSize * rgbquad_size;
  
      uint8_t * pCopyBuffer = new uint8_t[total_bytes];
  
  
  
      for (int x = 0; x < width; x++)
  
      {
  
          for (int y = 0; y < height; y++)
  
          {
  
              int index = (x + width * y) * rgbquad_size;
  
              int invertIndex = (x + width* (height - y - 1)) * rgbquad_size;
  
  
  
              //BGRA to RGBA
  
              pCopyBuffer[index] = buf[invertIndex + 2];
  
              pCopyBuffer[index + 1] = buf[invertIndex + 1];
  
              pCopyBuffer[index + 2] = buf[invertIndex];
  
              pCopyBuffer[index + 3] = 0xFF;
  
          }
  
      }
  
  
  
      return pCopyBuffer;
  
  }
  
  
  
  void GetDIBBuffer(Interface* ip, BITMAPINFO *bmi, uint8_t** outBuffer)
  
  {
  
      int size;
  
  
  
      ViewExp& view = ip->GetActiveViewExp();
  
  
  
      view.getGW()->getDIB(NULL, &size);
  
  
  
      bmi = (BITMAPINFO *)malloc(size);
  
      BITMAPINFOHEADER *bmih = (BITMAPINFOHEADER *)bmi;
  
      view.getGW()->getDIB(bmi, &size);
  
  
  
      uint8_t * pCopyBuffer = Util::ToUint8_t(bmi->bmiColors, bmih->biWidth, bmih->biHeight);
  
  
  
      *outBuffer = pCopyBuffer;
  
  }

  This function is used to get the DIB :

  void GetViewportDIB(Interface* ip, BITMAPINFO *bmi, BITMAPINFOHEADER *bmih, BitmapInfo biFile, Bitmap *map)
  
  {
  
      int size;
  
  
  
      if (!biFile.Name()[0])
  
          return;
  
  
  
      ViewExp& view = ip->GetActiveViewExp();
  
  
  
      view.getGW()->getDIB(NULL, &size);
  
  
  
      bmi = (BITMAPINFO *)malloc(size);
  
      bmih = (BITMAPINFOHEADER *)bmi;
  
  
  
      view.getGW()->getDIB(bmi, &size);
  
  
  
      biFile.SetWidth((WORD)bmih->biWidth);
  
      biFile.SetHeight((WORD)bmih->biHeight);
  
      biFile.SetType(BMM_TRUE_32);
  
  
  
      map = TheManager->Create(&biFile);
  
      map->OpenOutput(&biFile);
  
      map->FromDib(bmi);
  
      map->Write(&biFile);
  
      map->Close(&biFile);
  
  }

  And after the conversion to AVFrame and video encoding :

  The EncodeFromMem function is call each frame.

  int Converter::EncodeFromMem(const char *outputDir, int frameNumber, uint8_t* data)
  
  {
  
      int ret;
  
  
  
      inputFrame->pts = frameNumber;
  
      EncodeFrame(data, codecContext, inputFrame, &pkt, file);
  
  
  
      return 0;
  
  }
  
  
  
  static void RgbToYuv(uint8_t *rgb, AVCodecContext *c, AVFrame *frame)
  
  {
  
      struct SwsContext *swsCtx = NULL;
  
      const int in_linesize[1] = { 3 * c->width };// RGB stride
  
      swsCtx = sws_getCachedContext(swsCtx, c->width, c->height, AV_PIX_FMT_RGB24, c->width, c->height, AV_PIX_FMT_YUV420P, 0, 0, 0, 0);
  
      sws_scale(swsCtx, (const uint8_t * const *)&rgb, in_linesize, 0, c->height, frame->data, frame->linesize);
  
  }
  
  
  
  static void EncodeFrame(uint8_t *rgb, AVCodecContext *c, AVFrame *frame, AVPacket **pkt, FILE *file)
  
  {
  
      int ret, got_output;
  
  
  
      RgbToYuv(rgb, c, frame);
  
  
  
      *pkt = av_packet_alloc();
  
      av_init_packet(*pkt);
  
      (*pkt)->data = NULL;
  
      (*pkt)->size = 0;
  
  
  
      ret = avcodec_encode_video2(c, *pkt, frame, &got_output);
  
      if (ret < 0)
  
      {
  
          fprintf(stderr, "Error encoding frame/n");
  
          exit(1);
  
      }
  
      if (got_output)
  
      {
  
          fwrite((*pkt)->data, 1, (*pkt)->size, file);
  
          av_packet_unref(*pkt);
  
      }
  
  }

  To finish I have a function that write the packets and free the memory :
  This function is called once at the end of the time range.

  int Converter::Finalize()
  
  {
  
      int ret, got_output;
  
      uint8_t endcode[] = { 0, 0, 1, 0xb7 };
  
  
  
      /* get the delayed frames */
  
      do
  
      {
  
          fflush(stdout);
  
          ret = avcodec_encode_video2(codecContext, pkt, NULL, &got_output);
  
          if (ret < 0)
  
          {
  
              fprintf(stderr, "Error encoding frame/n");
  
              return 1;
  
          }
  
          if (got_output)
  
          {
  
              fwrite(pkt->data, 1, pkt->size, file);
  
              av_packet_unref(pkt);
  
          }
  
      } while (got_output);
  
  
  
      fwrite(endcode, 1, sizeof(endcode), file);
  
      fclose(file);
  
  
  
      avcodec_close(codecContext);
  
      av_free(codecContext);
  
  
  
      av_frame_unref(inputFrame);
  
      av_frame_free(&inputFrame);
  
      //av_freep(&inputFrame->data[0]); //Crash
  
  
  
      delete outputFilename;
  
      outputFilename = 0;
  
  
  
      return 0;
  
  }

  EDIT :

  I modify my RgbToYuv function and create another one to convert back the yuv frame to an rgb one.

  This not really solve the problem, but maybe focus the problem on the conversion from YuvToRgb.

  This is the result of the conversion from YUV to RGB :

   ![YuvToRgb result] : https://img42.com/kHqpt+

  static void YuvToRgb(AVCodecContext *c, AVFrame *frame)
  
  {
  
      struct SwsContext *img_convert_ctx = sws_getContext(c->width, c->height, AV_PIX_FMT_YUV420P, c->width, c->height, AV_PIX_FMT_RGB24, SWS_BICUBIC, NULL, NULL, NULL);
  
      AVFrame * rgbPictInfo = av_frame_alloc();
  
      avpicture_fill((AVPicture*)rgbPictInfo, *(frame)->data, AV_PIX_FMT_RGB24, c->width, c->height);
  
      sws_scale(img_convert_ctx, frame->data, frame->linesize, 0, c->height, rgbPictInfo->data, rgbPictInfo->linesize);
  
  
  
      Util::DebugWindow(c->width, c->height, rgbPictInfo->data[0]);
  
  }
  
  static void RgbToYuv(uint8_t *rgb, AVCodecContext *c, AVFrame *frame)
  
  {
  
      AVFrame * rgbPictInfo = av_frame_alloc();
  
      avpicture_fill((AVPicture*)rgbPictInfo, rgb, AV_PIX_FMT_RGBA, c->width, c->height);
  
  
  
      struct SwsContext *swsCtx = sws_getContext(c->width, c->height, AV_PIX_FMT_RGBA, c->width, c->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
  
      avpicture_fill((AVPicture*)frame, rgb, AV_PIX_FMT_YUV420P, c->width, c->height);    
  
      sws_scale(swsCtx, rgbPictInfo->data, rgbPictInfo->linesize, 0, c->height, frame->data, frame->linesize);
  
  
  
      YuvToRgb(c, frame);
  
  }

• x264 Building error - Android

  21 avril 2016, par Jay Parikh

  I am using this repository to build ffmpeg static library which includes x264,libpng and others, please
  visit this link https://github.com/writingminds/ffmpeg-android

  i am using windows 7 as host and ubuntu 15.10 (_64) as guest os using VMware Workstation 12
  and
  Android-ndk-r11b-linux-x86_64

  i do have Prebuilt libraries , but now i want it without PIE support

  i am getting this error in config.log in x264 folder while building
  through

  ./android_build.sh

  here is the log :

  x264 configure script
  
  Command line options: "--cross-prefix=/mnt/hgfs/uShare/ffmpeg-android/toolchain-android/bin/arm-linux 
  
  /mnt/hgfs/uShare/ffmpeg-android/toolchain-android/bin/arm-linux-androideabi-gcc 
  
  
  
  checking whether /mnt/hgfs/uShare/ffmpeg-android/toolchain-android/bin/arm-linux-androideabi-gcc 
  
  
  
  --sysroot=/mnt/hgfs/uShare/ffmpeg-android/toolchain-android/sysroot works... no
  
  
  
   Failed commandline was:
  
  
  
  --sysroot=/mnt/hgfs/uShare/ffmpeg-android/toolchain-android/sysroot conftest.c  -Wall -I. -I$(SRCPATH) --sysroot=/mnt/hgfs/uShare/ffmpeg-android/toolchain-android/sysroot    --sysroot=/mnt/hgfs/uShare/ffmpeg-android/toolchain-android/sysroot -lm -o conftest
  
  
  
  /mnt/hgfs/uShare/ffmpeg-android/toolchain-android/bin/../lib/gcc/arm-linux-androideabi/4.9/../../../../arm-linux-androideabi/bin/ld: fatal error:
  
  
  
  conftest: Input/output error
  
  
  
  Failed program was: 
  
  
  
  int main (void) {  return 0; }
  
  
  
  DIED: No working C compiler found.

  ushare is my shared folder between windows and ubuntu

  I have spend almost a week ,trying to solve every error i get.
  these errors are like never ending , 1 solution give 10 more errors
  i have researched a LOT for this library

  thanks a lot in advance.

  Also i thought that x264 library might have poroblem ,so i tried to disable it
  but next library "libpng" also had Same log Error

  i think problem is in Input/output error (obviously)
  this line in log kind of confuses me (those /../../)

  /mnt/hgfs/uShare/ffmpeg-android/toolchain-android/bin/../lib/gcc/arm-linux-androideabi/4.9/../../../../arm-linux-androideabi/bin/ld : fatal error :

  its like two folder overlaping address...

  thanks a lot in advance.
  please don’t go harsh on me ,its my first time,all thanks to this thing...