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• ffmpeg : programmatically use libavcodec and encode and decode raw bitmap, all in just few milliseconds and small compressed size on Raspberry Pi 4

  15 mars 2023, par Jerry Switalski

  We need to compress the size of the 1024x2048 image we produce, to size of about jpeg (200-500kb) from raw 32bits RGBA (8Mb) on Raspberry Pi 4. All in c/c++ program.

  


  The compression needs to be just in few milliseconds, otherwise it is pointless to us.

  


  We decided to try supported encoding using ffmpeg dev library and c/c++ code.

  


  The problem we are facing is that when we edited example of the encoding, provided by ffmpeg developers, the times we are dealing are unacceptable.

  


  Here you can see the edited code where the frames are created :

  


  for (i = 0; i < 25; i++)
{
#ifdef MEASURE_TIME
        auto start_time = std::chrono::high_resolution_clock::now();
        std::cout << "START Encoding frame...\n";
#endif
    fflush(stdout);

    ret = av_frame_make_writable(frame);
    if (ret < 0)
        exit(1);

    //I try here, to convert our 32 bits RGBA image to YUV pixel format:

    for (y = 0; y < c->height; y++)
    {
        for (x = 0; x < c->width; x++)
        {
            int imageIndexY = y * frame->linesize[0] + x;

            uint32_t rgbPixel = ((uint32_t*)OutputDataImage)[imageIndexY];

            double Y, U, V;
            uint8_t R = rgbPixel << 24;
            uint8_t G = rgbPixel << 16;
            uint8_t B = rgbPixel << 8;

            YUVfromRGB(Y, U, V, (double)R, (double)G, (double)B);
            frame->data[0][imageIndexY] = (uint8_t)Y;

            if (y % 2 == 0 && x % 2 == 0)
            {
                int imageIndexU = (y / 2) * frame->linesize[1] + (x / 2);
                int imageIndexV = (y / 2) * frame->linesize[2] + (x / 2);

                frame->data[1][imageIndexU] = (uint8_t)U;
                frame->data[2][imageIndexV] = (uint8_t)Y;
            }
        }
    }

    frame->pts = i;

    /* encode the image */
    encode(c, frame, pkt, f);

#ifdef MEASURE_TIME
        auto end_time = std::chrono::high_resolution_clock::now();
        auto time = end_time - start_time;
        std::cout << "FINISHED Encoding frame in: " << time / std::chrono::milliseconds(1) << "ms.\n";

#endif
    }


  


  Here are some important parts of the previous parts of that function :

  


  codec_name = "mpeg4";

codec = avcodec_find_encoder_by_name(codec_name);

c = avcodec_alloc_context3(codec);
    
c->bit_rate = 1000000;  
c->width = IMAGE_WIDTH;
c->height = IMAGE_HEIGHT;
c->gop_size = 1;
c->max_b_frames = 1;
c->pix_fmt = AV_PIX_FMT_YUV420P;   


  


  IMAGE_WIDTH and IMAGE_HEIGHT are 1024 and 2048 corresponding.

  


  The result I have ran on Raspberry Pi 4 look like this :

  


  START Encoding frame...
Send frame   0
FINISHED Encoding frame in: 40ms.
START Encoding frame...
Send frame   1
Write packet   0 (size=11329)
FINISHED Encoding frame in: 60ms.
START Encoding frame...
Send frame   2
Write packet   1 (size=11329)
FINISHED Encoding frame in: 58ms.


  


  Since I am completely green in encoding and using codecs, my question will be how to do it the best way and correct way, meaning the way which would reduce timing to few ms, and I am not sure the codec was chosen the best for the job, or the pixel format.

  


  The rest of the meaningful code you can see here (the encode() function you can find in the ffmpeg developer example I gave link to above) :

  


  void RGBfromYUV(double& R, double& G, double& B, double Y, double U, double V)
{
    Y -= 16;
    U -= 128;
    V -= 128;
    R = 1.164 * Y + 1.596 * V;
    G = 1.164 * Y - 0.392 * U - 0.813 * V;
    B = 1.164 * Y + 2.017 * U;
}


  


• how to find video and audio stream times without the deprecated values ? libav 10.5

  23 novembre 2014, par Narayana James Emery

  After looking into the documentation, AVStream.pts has been deprecated. Before I was using this loop to try and get the video and audio time. it’s the same as whats in the api-example.c (which no longer works) :

  if (audioStream_)
  
      {
  
          VideoTime = (double)videoStream_->pts.val*videoStream_->time_base.num/videoStream_->time_base.den;
  
          do
  
          {
  
              AudioTime = (double)audioStream_->pts.val*audioStream_->time_base.num/audioStream_->time_base.den;
  
              ret = WriteAudioFrame();
  
          }
  
          while (AudioTime < VideoTime && ret);
  
          if (ret < 0)
  
              return ret;
  
      }

  what is the current alternative ? I haven’t been able to get anything to work as of yet and I’ve been searching for around 3 hours.

• avfilter/vf_ssim360 : Use correct type in sizeof

  12 mars 2023, par Andreas Rheinhardt

  avfilter/vf_ssim360 : Use correct type in sizeof
  SSIM360Context.ssim360_hist is an array of four pointers to double ;
  
  so sizeof(*ssim360_hist[0]) (=sizeof(double)) is the correct size
  
  to use to calculate the amount of memory to allocate, not
  
  sizeof(*ssim360_hist) (which is sizeof(double*)).
  Use FF_ALLOCZ_TYPED_ARRAY to avoid this issue altogether.
  Fixes Coverity issue #1520671.
  Reviewed-by : Anton Khirnov <anton@khirnov.net>
  
  Reviewed-by : Jan Ekström <jeebjp@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavfilter/vf_ssim360.c