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• Decoded YUV shows green edge when rendered with OpenGL

  2 février 2023, par Alex

  Any idea, why decoded YUV -> RGB(shader conversion) has that extra green edge on the right side ?
  
Almost any 1080X1920 video seems to have this issue.

  


  

  


  A screen recording of the issue is uploaded here https://imgur.com/a/JtUZq4h

  


  Once I manually scale up the texture width, I can see it fills up to the viewport, but it would be nice if I could fix the actual cause. Is it some padding that's part of YUV colorspace ? What else could it be ?

  


  My model is -1 to 1, filling the entire width
  
The texture coordinates are also 0 to 1 ratio

  


  float vertices[] = {
    -1.0, 1.0f, 0.0f, 0.0,     // top left
     1.0f, 1.0f, 1.0, 0.0,      // top right
    -1.0f, -1.0f, 0.0f, 1.0f,  // bottom left
     1.0f, -1.0f, 1.0f, 1.0f    // bottom right
};


  


  Fragment Shader

  


  #version 330 core

in vec2 TexCoord;

out vec4 FragColor;
precision highp float;
uniform sampler2D textureY;
uniform sampler2D textureU;
uniform sampler2D textureV;
uniform float alpha;
uniform vec2 texScale;


void main()
{
    float y = texture(textureY, TexCoord / texScale).r;
    float u = texture(textureU, TexCoord / texScale).r - 0.5; 
    float v = texture(textureV, TexCoord / texScale).r - 0.5;
    
    vec3 rgb;
    
    //yuv - 709
    rgb.r = clamp(y + (1.402 * v), 0, 255);
    rgb.g = clamp(y - (0.2126 * 1.5748 / 0.7152) * u - (0.0722 * 1.8556 / 0.7152) * v, 0, 255);
    rgb.b = clamp(y + (1.8556 * u), 0,255);

    FragColor = vec4(rgb, 1.0);
} 


  


  Texture Class

  


  class VideoTexture {
   public:
    VideoTexture(Decoder *dec) : decoder(dec) {
        glGenTextures(1, &texture1);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glBindTexture(GL_TEXTURE_2D, texture1);
        glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, decoder->frameQueue.first().linesize[0], decoder->frameQueue.first().height, 0, format, GL_UNSIGNED_BYTE, 0);
        glGenerateMipmap(GL_TEXTURE_2D);

        glGenTextures(1, &texture2);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glBindTexture(GL_TEXTURE_2D, texture2);
        glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, decoder->frameQueue.first().linesize[1], decoder->frameQueue.first().height / 2, 0, format, GL_UNSIGNED_BYTE, 0);
        glGenerateMipmap(GL_TEXTURE_2D);

        glGenTextures(1, &texture3);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glBindTexture(GL_TEXTURE_2D, texture3);
        glTexImage2D(GL_TEXTURE_2D, 0, internalFormat, decoder->frameQueue.first().linesize[2], decoder->frameQueue.first().height / 2, 0, format, GL_UNSIGNED_BYTE, 0);
        glGenerateMipmap(GL_TEXTURE_2D);
    }

    void Render(Shader *shader, Gui *gui) {
        if (decoder->frameQueue.isEmpty()) {
            return;
        }

        glActiveTexture(GL_TEXTURE0);
        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, decoder->frameQueue.first().linesize[0], decoder->frameQueue.first().height, format, GL_UNSIGNED_BYTE, decoder->frameQueue.at(currentFrame).data[0]);
        glBindTexture(GL_TEXTURE_2D, texture1);
        shader->setInt("textureY", 0);

        glActiveTexture(GL_TEXTURE1);
        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, decoder->frameQueue.first().linesize[1], decoder->frameQueue.first().height / 2, format, GL_UNSIGNED_BYTE, decoder->frameQueue.at(currentFrame).data[1]);
        glBindTexture(GL_TEXTURE_2D, texture2);
        shader->setInt("textureU", 1);

        glActiveTexture(GL_TEXTURE2);
        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, decoder->frameQueue.first().linesize[2], decoder->frameQueue.first().height / 2, format, GL_UNSIGNED_BYTE, decoder->frameQueue.at(currentFrame).data[2]);
        glBindTexture(GL_TEXTURE_2D, texture3);
        shader->setInt("textureV", 2);
    }

    ~VideoTexture() {
        printf("\nVideo texture destructor");
        glDeleteTextures(1, &texture1);
        glDeleteTextures(1, &texture2);
        glDeleteTextures(1, &texture3);
    }

   private:
    GLuint texture1;
    GLuint texture2;
    GLuint texture3;
    GLint internalFormat = GL_RG8;
    GLint format = GL_RED;
    int currentFrame = 0;
    Decoder *decoder;
}


  


• How to define an in-memory object for opengl to render

  23 novembre 2016, par Ted Yu

  Currently I’m working on an android application, in which I want to fetch frames from Camera, render off-screen and encode into a video. I took the ideas from grafika, camera and egl context works well. However, MediaCodec does not function for some reasons, so I turn to ffmpeg. I do as follows :

  1. Open camera in camera thread
  2. Setup egl context in egl thread, create an off-screen surface
  3. Setup ffmpeg encoder/muxer in encode thread
  4. Generate texture and new a SurfaceTexture backed with that texture in egl thread, and pass the SurfaceTexture to the camera thread for previewing
  5. Everytime SurfaceTexture has frame available, draw the texture to the off-screen surface in egl thread
  6. Read pixels with glReadPixels to a buffer, and pass the buffer to the encode thread
  7. Encode video in the encode thread if there is any available frames

  Everything works fine without glReadPixels, and performance goes low with the glReadPixels invokation uncommented, even the encode thread is not running.

  grafika gets high performance by drawing on MediaCodec’s input surface (see VideoEncoderCore).

  So I wonder how to do the same thing with ffmpeg ? Is it possible to allocating a frame buffer for rendering and encoding, so that I can get rid of glReadPixels (memory copying) ?

• Scroll seamless image with FFMPEG

  22 septembre 2022, par Rob

  I want to create a video from a single image. The image should scroll vertically and the output needs to be seamless so it can be looped (the image itself is seamless).

  


  Example of what I want to create :
GIF example
and the texture from the example : seamless texture.

  


  Length of the video is not that important since if the scrolling is seamless I should be able to just loop it with ffmpeg -stream_loop 3 -i input.mp4 -c copy output.mp4 afterwards.

  


  I have tried :

  


  ffmpeg -loop 1 -i input.png -framerate 30 -vf "scroll=vertical=0.002,crop=iw:600:0:0,format=yuv420p" -t 10 -y output.mp4


  


  which creates a video with the desired scrolling effect but its not seamless due to Issues matching the video length with the height of the image/scrolling speed and it looks something like this : Example output (exaggerated) Also ignore it scrolls the other way.

  


  I'm not sure how to proceed, maybe its just a simple math that needs to be done to add to
-t X by looking at the scroll speed & image height ? . Any ideas welcome how to solve this with either ffmpeg/python/powershell under windows.