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• avcodec_decode_video2 fails to decode after frame resolution change

  10 avril 2021, par Krzysztof Kansy

  I'm using ffmpeg in Android project via JNI to decode real-time H264 video stream. On the Java side I'm only sending the the byte arrays into native module. Native code is running a loop and checking data buffers for new data to decode. Each data chunk is processed with :
  

  



  int bytesLeft = data->GetSize();
int paserLength = 0;
int decodeDataLength = 0;
int gotPicture = 0;
const uint8_t* buffer = data->GetData();
while (bytesLeft > 0) {
    AVPacket packet;
    av_init_packet(&packet);
    paserLength = av_parser_parse2(_codecPaser, _codecCtx, &packet.data, &packet.size, buffer, bytesLeft, AV_NOPTS_VALUE, AV_NOPTS_VALUE, AV_NOPTS_VALUE);
    bytesLeft -= paserLength;
    buffer += paserLength;

    if (packet.size > 0) {
        decodeDataLength = avcodec_decode_video2(_codecCtx, _frame, &gotPicture, &packet);
    }
    else {
        break;
    }
    av_free_packet(&packet);
}

if (gotPicture) {
// pass the frame to rendering
}


  



  The system works pretty well until incoming video's resolution changes. I need to handle transition between 4:3 and 16:9 aspect ratios. While having AVCodecContext configured as follows :

  



  _codecCtx->flags2|=CODEC_FLAG2_FAST;
_codecCtx->thread_count = 2;
_codecCtx->thread_type = FF_THREAD_FRAME;

if(_codec->capabilities&CODEC_FLAG_LOW_DELAY){
    _codecCtx->flags|=CODEC_FLAG_LOW_DELAY;
}


  



  I wasn't able to continue decoding new frames after video resolution change. The got_picture_ptr flag that avcodec_decode_video2 enables when whole frame is available was never true after that.
  
This ticket made me wonder if the issue isn't connected with multithreading. Only useful thing I've noticed is that when I change thread_type to FF_THREAD_SLICE the decoder is not always blocked after resolution change, about half of my attempts were successfull. Switching to single-threaded processing is not possible, I need more computing power. Setting up the context to one thread does not solve the problem and makes the decoder not keeping up with processing incoming data.
  
Everything work well after app restart.
  

  



  I can only think of one workoround (it doesn't really solve the problem) : unloading and loading the whole library after stream resolution change (e.g as mentioned in here). I don't think it's good tho, it will propably introduce other bugs and take a lot of time (from user's viewpoint).

  



  Is it possible to fix this issue ?

  



  EDIT :
  
I've dumped the stream data that is passed to decoding pipeline. I've changed the resolution few times while stream was being captured. Playing it with ffplay showed that in moment when resolution changed and preview in application froze, ffplay managed to continue, but preview is glitchy for a second or so. You can see full ffplay log here. In this case video preview stopped when I changed resolution to 960x720 for the second time. (Reinit context to 960x720, pix_fmt: yuv420p in log).

  


• avcodec_decode_video2 fails to decode after frame resolution change

  7 octobre 2016, par Krzysztof Kansy

  I’m using ffmpeg in Android project via JNI to decode real-time H264 video stream. On the Java side I’m only sending the the byte arrays into native module. Native code is running a loop and checking data buffers for new data to decode. Each data chunk is processed with :
  

  int bytesLeft = data->GetSize();
  
  int paserLength = 0;
  
  int decodeDataLength = 0;
  
  int gotPicture = 0;
  
  const uint8_t* buffer = data->GetData();
  
  while (bytesLeft > 0) {
  
      AVPacket packet;
  
      av_init_packet(&packet);
  
      paserLength = av_parser_parse2(_codecPaser, _codecCtx, &packet.data, &packet.size, buffer, bytesLeft, AV_NOPTS_VALUE, AV_NOPTS_VALUE, AV_NOPTS_VALUE);
  
      bytesLeft -= paserLength;
  
      buffer += paserLength;
  
  
  
      if (packet.size > 0) {
  
          decodeDataLength = avcodec_decode_video2(_codecCtx, _frame, &gotPicture, &packet);
  
      }
  
      else {
  
          break;
  
      }
  
      av_free_packet(&packet);
  
  }
  
  
  
  if (gotPicture) {
  
  // pass the frame to rendering
  
  }

  The system works pretty well until incoming video’s resolution changes. I need to handle transition between 4:3 and 16:9 aspect ratios. While having AVCodecContext configured as follows :

  _codecCtx->flags2|=CODEC_FLAG2_FAST;
  
  _codecCtx->thread_count = 2;
  
  _codecCtx->thread_type = FF_THREAD_FRAME;
  
  
  
  if(_codec->capabilities&CODEC_FLAG_LOW_DELAY){
  
      _codecCtx->flags|=CODEC_FLAG_LOW_DELAY;
  
  }

  I wasn’t able to continue decoding new frames after video resolution change. The got_picture_ptr flag that avcodec_decode_video2 enables when whole frame is available was never true after that.
  This ticket made me wonder if the issue isn’t connected with multithreading. Only useful thing I’ve noticed is that when I change thread_type to FF_THREAD_SLICE the decoder is not always blocked after resolution change, about half of my attempts were successfull. Switching to single-threaded processing is not possible, I need more computing power. Setting up the context to one thread does not solve the problem and makes the decoder not keeping up with processing incoming data.
  Everything work well after app restart.
  

  I can only think of one workoround (it doesn’t really solve the problem) : unloading and loading the whole library after stream resolution change (e.g as mentioned in here). I don’t think it’s good tho, it will propably introduce other bugs and take a lot of time (from user’s viewpoint).

  Is it possible to fix this issue ?

  EDIT :
  I’ve dumped the stream data that is passed to decoding pipeline. I’ve changed the resolution few times while stream was being captured. Playing it with ffplay showed that in moment when resolution changed and preview in application froze, ffplay managed to continue, but preview is glitchy for a second or so. You can see full ffplay log here. In this case video preview stopped when I changed resolution to 960x720 for the second time. (Reinit context to 960x720, pix_fmt: yuv420p in log).

• Render FFmpeg AVFrame as OpenGL texture ?

  5 mars 2019, par ZeroDefect

  I’m attempting to to render a jpeg image (1024x1024 pixels) in the form of an FFmpeg AVFrame as a texture in OpenGL. What I get instead is something that appears as a 1024x1024 dark green quad :

  

  The code to render the AVFrame data in OpenGL is shown below. I have convinced myself that the raw RGB data held within the FFmpeg AVFrame data is not solely dark green.

  GLuint g_texture = {};
  
  
  
  //////////////////////////////////////////////////////////////////////////
  
  void display()
  
  {
  
      // Clear color and depth buffers
  
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  
      glMatrixMode(GL_MODELVIEW);     // Operate on model-view matrix
  
  
  
      glEnable(GL_TEXTURE_2D);
  
      GLuint texture = g_texture;
  
      glBindTexture(GL_TEXTURE_2D, texture);
  
  
  
      // Draw a quad
  
      glBegin(GL_QUADS);
  
      glVertex2i(0, 0); // top left
  
      glVertex2i(1024, 0); // top right
  
      glVertex2i(1024, 1024); // bottom right
  
      glVertex2i(0, 1024); // bottom left
  
      glEnd();
  
  
  
      glDisable(GL_TEXTURE_2D);
  
      glBindTexture(GL_TEXTURE_2D, 0);
  
  
  
      glFlush();
  
  }
  
  
  
  /* Initialize OpenGL Graphics */
  
  void initGL(int w, int h)
  
  {
  
      glViewport(0, 0, w, h); // use a screen size of WIDTH x HEIGHT
  
      glEnable(GL_TEXTURE_2D);     // Enable 2D texturing
  
  
  
      glMatrixMode(GL_PROJECTION);     // Make a simple 2D projection on the entire window
  
      glOrtho(0.0, w, h, 0.0, 0.0, 100.0);
  
      glMatrixMode(GL_MODELVIEW);    // Set the matrix mode to object modeling
  
      //glTranslatef( 0, 0, -15 );
  
  
  
      glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
  
      glClearDepth(0.0f);
  
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear the window
  
  }
  
  
  
  //////////////////////////////////////////////////////////////////////////
  
  int main(int argc, char *argv[])
  
  {
  
      std::shared_ptr<avframe> apAVFrame;
  
      if (!load_image_to_AVFrame(apAVFrame, "marble.jpg"))
  
      {
  
          assert(false);
  
          return 1;
  
      }
  
  
  
      // From here on out, the AVFrame is RGB interleaved
  
      // and is sized to 1,024 x 1,024 (power of 2).
  
  
  
      glutInit(&amp;argc, argv);
  
      glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
  
      glutInitWindowSize(1060, 1060);
  
      glutInitWindowPosition(0, 0);
  
      glutCreateWindow("OpenGL - Creating a texture");
  
  
  
      glGenTextures(1, &amp;g_texture);
  
  
  
      //glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
  
      glBindTexture(GL_TEXTURE_2D, g_texture);
  
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, apAVFrame->width,
  
                   apAVFrame->height, 0, GL_RGB, GL_UNSIGNED_BYTE,
  
                   apAVFrame->data[0]);
  
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); /* We will use linear interpolation for magnification filter */
  
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); /* We will use linear interpolation for minifying filter */
  
  
  
      initGL(1060, 1060);
  
  
  
      glutDisplayFunc(display);
  
  
  
      glutMainLoop();
  
  
  
      return 0;
  
  }
  
  </avframe>

  Environment :

  • Ubuntu 18.04
  • GCC v8.2

  EDIT : As per @immibis’ suggestion below, it all works when I change the rendering of the quad to :

  // Draw a quad
  
  glBegin(GL_QUADS);
  
  glTexCoord2f(0, 0);
  
  glVertex2i(0, 0); // top left
  
  glTexCoord2f(1, 0);
  
  glVertex2i(1024, 0); // top right
  
  glTexCoord2f(1, 1);
  
  glVertex2i(1024, 1024); // bottom right
  
  glTexCoord2f(0, 1);
  
  glVertex2i(0, 1024); // bottom left
  
  glEnd();