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• ffmpeg Cg shader ITU 709 YCbYg

  22 juillet 2018, par user2517097

  I have a viewer (mrViewer at sourceforge) that displays movie files by feeding YCbCr images and merging them later in a shader. Currently I am trying to track a color issue in my viewer, not displaying DNxHD movies properly. The EXR file is to be seen in RGB, not scene linear. The movie was created from that EXR file in Nuke (a comp program). All movie files are converted from EXR image without color space conversion in NUKE 11. All movie files are encoded with video color range.

  Color_Profile_nuke11.exr

  Color_Profile_nuke11_DNxHD_mov64_444.mov

  Color_Profile_nuke11_DNxHD_mov64_422.mov

  In the shader, I do (simplified Cg code) :

    half3 pre;
  
  
  
    pre.r = tex2D(YImage, tc).r;  // Y
  
    pre.g = tex2D(UImage, tc).r;  // U
  
    pre.b = tex2D(VImage, tc).r;  // V
  
  
  
    half3 c;
  
  
  
    if ( coeffs )
  
    {
  
        pre += Koff;
  
  
  
        c.r = dot(Kr, pre);
  
        c.g = dot(Kg, pre);
  
        c.b = dot(Kb, pre);
  
    }
  
    else
  
    {
  
  
  
        half3 yuv;
  
  
  
        yuv.r = 1.1643 * ( pre.r - 0.0625 );
  
        yuv.g = pre.g - 0.5;
  
        yuv.b = pre.b - 0.5;
  
  
  
        c.r = yuv.r + 1.5958 * yuv.b;
  
        c.g = yuv.r - 0.39173 * yuv.g - 0.81290 * yuv.b;
  
        c.b = yuv.r + 2.017 * yuv.g;
  
    }
  
  
  
    Out output;
  
    output.pixel = c;
  
    return output;
  
  
  
  
  
  
  
  // Send coeffs to shader shader (C++ code)
  
  {
  
  _shader->setUniform( "coeffs", 1 );
  
  // HDTV  YCbCr coefficients
  
  _shader->setUniform( "Koff", 0.0f, -0.5f, -0.5f );
  
  _shader->setUniform( "Kr", 1.0f, 0.0f, 1.28033f );
  
  _shader->setUniform( "Kg", 1.0f, -0.21482f, -0.38059f );
  
  _shader->setUniform( "Kb", 1.0f, 2.12798f, 0.0f );
  
  }

  Now, my problem is that the ITU 709 (the one with the dot() calls) path seems to not be behaving properly. It creates a washed out image. I am wondering if this has to do with full jpeg and full mpeg not having taken into account or whether my coefficients are wrong.

  If I set the color matrix to ITU709 in my C++ code with the ffmpeg library and let its swscale do the conversion, I get good color correspondence in the image if I select the (default) 601 path in the shader.

• How to make cropping when doing motion-tracking look super smooth ? (using cv2 and yolo v8)

  4 décembre 2024, par Thomas Lancer

  I'm using yolo to track a face in a video on a frame by frame basis, and then I'm using cv2 to crop the video (with some padding) around the speakers face so it creates a motion tracking type effect. (short example here : https://www.instagram.com/reel/DCIFkFEObkE/?hl=en)

  


  The problem I'm running into is my final crop looks "shaky". Like it's flickering a bit. I think this is because every frame yolo is updating the coordinates, and so there's a slight change in x, y and because of that it creates this shakiness/flickering effect. Here's what mine looks like compared to the example : https://drive.google.com/file/d/1MKHWK-5EH5abSq6i32r71GWld76tN1GP/view?usp=sharing

  


  You can see there's this "shakiness" type look to it. it's especially apparent when the speaker is relatively still.

  


  I've tried doing an exponential moving average and a few other averaging techniques but none have fixed it.

  


  Is my fundamental approach of doing a frame by frame crop wrong ? or is there just some smoothing algorithm or some dumb mistake that you think I may be making ? Any advice is mega appreciated !

  


• ffmpeg stream rc buffer underflow

  5 août 2015, par finder2

  At the moment I’m setting up a screen-sharing platform with the opensource tool ffmpeg / ffserver. At the beginning of the sharing everything is fine. After around 1 1/2 minutes I get the following exception in the output.

  [flv @ 0x3a47aa0] rc buffer underflow
[flv @ 0x3a47aa0] max bitrate possibly too small or try trellis with large lmax or increase qmax

  I’ve tried to set an verry high lmax & qmax but this hasn’t changed any thing.Additionally I’ve tried to increase the bitrate , the buffersize and the bitrate.

  I use the following command with ffmpeg :

  ffmpeg -f x11grab -s 1920x1080 -r 20 -i :0.0+1680,0 "http://localserver.de:8080/input1.ffm"

  The config file for the ffserver is :

  HTTPPort 8080
  
  HTTPBindAddress 0.0.0.0
  
  MaxHTTPConnections 2000
  
  MaxClients 1000
  
  MaxBandwidth 50000
  
  CustomLog -
  
  
  
  <feed>
  
    File /var/ffserver/input1.ffm
  
    FileMaxSize 20M
  
    ACL allow *FROM IP*  *TO IP* 
  
  </feed>
  
  
  
  <stream>
  
    Feed input1.ffm
  
    Format swf
  
    VideoCodec flv
  
    VideoFrameRate 20
  
    VideoBufferSize 8000
  
    VideoBitRate 250
  
    VideoQMin 1
  
    VideoQMax 5
  
    VideoSize 640x400
  
    PreRoll 0
  
    StartSendOnKey
  
    NoAudio
  
  </stream>

  An other streaming format would also be a possibility but I didn’t know which are possible for live-streaming.

  Thanks in advanced

  efinder2