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• Is there a way to apply a curve bend in ffmpeg ?

  25 mars 2020, par stevendesu

  I have four cameras each feeding me a different portion of a basketball court. Due to the slight offset of the cameras physical locations and lens distortion around the edges of the camera, I cannot simply stitch the videos together without some kind of correction.

  I’ve looked into ffmpeg’s perspective filter, as well as the lenscorrection filter. In the former case it was only able to create a trapezoid, not the curved image I want. In the latter case using negative values to k1 and k2 seemed to be heading in the right direction, but it either disorted the top and bottom of the image to the point of being nonsensical noise, or it zoomed in to the image so much that I lost important details.

  For the sample picture below, ultimately I want the midcourt line (the blue vertical line on the right side) to be vertical, and I want the mess of wires on the white desk at the bottom to remain visible and identifiable.

  Given a video which looks like the following :

  

  I wish to produce something like the following :

  

  This image was made using the "Curve Bend" filter in GIMP, but I just eye-balled it - so it’s not perfect. Ideally once I get the exact parameters the midcourt line will be perfectly vertical

  When using the lenscorrection filter, no values for k1 and k2 seemed to get the effect I want :

  Negative k1, negative k2 :

  

  Negative k1, positive k2 :

  

  Positive k1, negative k2 :

  

  Positive k1, positive k2 :

  

  In general :

  • negative / negative distorted the image beyond recognition
  • negative / positive looked alright, but the midcourt line was off the screen and it wasn’t clear if any distortion had been applied
  • positive / negative looked the best, but while the top and bottom curved in the middle of the left and right actually bulged out, leaving the midcourt line distorted
  • positive / positive was the opposite of the desired effect

• Some bugs when using SDL2 and ffmpeg to make a video player

  1er juin 2017, par trycatch

  used sws_scale to resize the image, and SDL2.0 to render, pixel format is YUV420P.

  1.When I Create SDL Render with SDL_RENDERER_SOFTWARE, I Get a black image like this :enter image description here, the top-left corner has a green point ;
  But When I Create SDL Render with SDL_RENDERER_ACCELERATED, I can See normal image ;

  2.When I resize the window, the player will crash on SDL_UpdateYUVTexture. I check width, height and linesize of the data, everything is OK.

  WHY ?

  Key Code :

  if (swscale_.frame.width % 2) 
  
    swscale_.frame.width -= 1;
  
  
  
  swscale_.free();
  
  swscale_.context = sws_getContext(
  
          vcodec->width, vcodec->height, vcodec->pix_fmt,
  
          swscale_.frame.width, swscale_.frame.height,
  
          AV_PIX_FMT_YUV420P, SWS_BICUBIC, nullptr, nullptr, nullptr);
  
  
  
  if (!swscale_.context)
  
      throw std::runtime_error("sws_getContext.");
  
  
  
  if (swscale_.frame.avframe)
  
    av_frame_free(&swscale_.frame.avframe);
  
  swscale_.frame.avframe = av_frame_alloc();
  
  unsigned char* out_buffer = (unsigned char *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, swscale_.frame.width, swscale_.frame.height, 1)+16);
  
  unsigned char* tmp = &out_buffer[16 - (unsigned long long)out_buffer % 16];
  
  av_image_fill_arrays(swscale_.frame.avframe->data, swscale_.frame.avframe->linesize, tmp,
  
    AV_PIX_FMT_YUV420P, swscale_.frame.width, swscale_.frame.height, 1);
  
  
  
  sws_scale(swscale_.context, (const unsigned char* const*)vframe_->data, vframe_->linesize, 
  
    0, vframe_->height,
  
    swscale_.frame.avframe->data, swscale_.frame.avframe->linesize);
  
  
  
  self.onRenderHandle(swscale_.frame);

  Code of SDL rendering :

  void Player::onRender(const frame& frame)
  
  {
  
    if (sdl_lock_.try_lock()) {
  
      ::ValidateRect(native_window_, NULL);
  
      if (frame.width != scr_width_ || frame.height != scr_height_) {
  
        scr_width_ = frame.width; scr_height_ = frame.height;
  
        SDL_SetWindowSize(screen_, scr_width_ + 2, scr_height_ + 2);
  
        SDL_DestroyRenderer(sdl_renderer_);
  
        sdl_renderer_ = SDL_CreateRenderer(screen_, -1, 0);
  
        video_texture_ = SDL_CreateTexture(sdl_renderer_, SDL_PIXELFORMAT_IYUV,
  
          SDL_TEXTUREACCESS_STREAMING, scr_width_, scr_height_);
  
      }
  
      SDL_UpdateYUVTexture(video_texture_, NULL,
  
        frame.avframe->data[0], frame.avframe->linesize[0],
  
        frame.avframe->data[1], frame.avframe->linesize[1],
  
        frame.avframe->data[2], frame.avframe->linesize[2]);
  
      sdl_lock_.unlock();
  
      ::InvalidateRect(native_window_, NULL, false);
  
    }
  
  }
  
  void Player::onPaint()
  
  {
  
    std::lock_guard lock(sdl_lock_);
  
    SDL_RenderClear(sdl_renderer_);
  
    SDL_RenderCopy(sdl_renderer_, video_texture_, NULL, NULL);
  
    SDL_RenderPresent(sdl_renderer_);
  
  }

• node js (or other) as streaming server

  20 décembre 2013, par Abdul Ali

  Apologies if a simple question but cannot find anything helpful . Am also new to the streaming concept.

  Goal is to set up a server which keeps on listening for data on a speific port. The user will be sending sequence of images from their iphone (# of images unknown).

  when the data is receieved, ffmpeg should start to get data from that port (as input) and send those images to ffserver to be streamed as a live video.

  did try Nginx-Rtmp module but the iphone developer have informed that in iphone, only ip and port can be given to open a stream (and no other part of the url can be given e.g. streamname and application name in case of nginx-rtmp)

  Any help and guide will be appreciatd that what can be used to set up a free and very simple sever that simply receives the images which ffmpeg can capture and send to ffserver .