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• Using SDL2 Render Pixels to create video using ffmpeg

  7 juillet 2024, par Riptide

  I made a small animation using SDL2 and I want to use ffmpeg to convert it to an h264 encoded video. I'm getting the texture RGBA pixels using SDL_RenderReadPixels and sending them to ffmpeg for rendering. The video does render, but is all messed up. The following is my code

  


  Spawning ffmpeg

  


  int child_pipe[2];

if (pipe(child_pipe) < 0) {
    perror("child_pipe");
}

printf("child_pipe[0]: %d, child_pipe[1]: %d\n", child_pipe[0], child_pipe[1]);

args.ffmpeg = &(FFMpeg){.std_in = child_pipe[WRITE_END]};

child_pid = fork();

printf("child: %d\n", child_pid);

if (child_pid == 0) {
    close(child_pipe[WRITE_END]);

    if (dup2(child_pipe[READ_END], STDIN_FILENO) < 0) {
        perror("dup2");
        return -1;
    }

    char *argv[] = {"ffmpeg",  "-loglevel", "verbose", "-y",   "-f",      "rawvideo", "-pixel_format", "rgba",      "-s",
                    "894x702", "-i",        "-",       "-c:v", "libx264", "-pix_fmt", "yuv420p",       "thing.mp4", NULL};

    int x = execvp("ffmpeg", argv);

    if (x != 0) {
        perror("execv");
        return x;
    }

    return -1;
}




  


  Here's how I render into SDL2 renderer. The rendering on SDL2 has no issues. In here I get the render pixels and send them to ffmpeg.

  


  void render_image(SDL_Renderer *renderer, int array[], size_t array_size, Image *image, FFMpeg *ffmpeg) {
    SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
    SDL_RenderClear(renderer);

    for (int i = 0; i < array_size; i++) {
        paint_image_strip(renderer, image, i, array[i]);
    }

    if (ANIMATION_DELAY_MS > 0) {
        SDL_Delay(ANIMATION_DELAY_MS);
    }

    if (ffmpeg != NULL) {
        int size = image->width * image->height * sizeof(Uint32);
        Uint32 *pixels = (Uint32 *)malloc(size);

        if (pixels == NULL) {
            printf("Malloc failed. Buy more ram\n");
            return;
        }

        int ret = SDL_RenderReadPixels(renderer, NULL, SDL_PIXELFORMAT_RGBA8888, pixels, image->width * sizeof(Uint32));

        if (ret != 0) {
            fprintf(stderr, "SDL_RenderReadPixels failed: %s\n", SDL_GetError());
            free(pixels);
        }

        int n = write(ffmpeg->std_in, image->img_data, size);

        if (n < 0) {
            perror("write failed");
        }

        free(pixels);
    }

    SDL_RenderPresent(renderer);
}



  


  Here's the issue. Here is what I see in SDL2 window

  


  

  


  and this is what ffmpeg renders


  


  there are inklings of the original image here. I thought it was an issue with RGBA vs ARGB but on double checking that wasn't the case.

  


  Expecting proper ffmpeg rendering.

  


• vf_colorchannelmixer : round lut entries to nearest

  14 mai 2013, par Michael Niedermayer

  vf_colorchannelmixer : round lut entries to nearest
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavfilter/vf_colorchannelmixer.c
  • [DH] tests/ref/fate/filter-colorchannelmixer

• Round number of bits read to next byte

  4 décembre 2014, par watwat2014

  I have a header that can be any number of bits, and there is a variable called ByteAlign that’s calculated by subtracting the current file position from the file position at the beginning of the file, the point of this variable is to pad the header to the next complete byte. so if the header is taking up 57 bits, the ByteAlign variable needs to be 7 bits in length to pad the header to 64 bits total, or 8 bytes.

  Solutions that don’t work :

  Variable % 8 - 8, the result is the answer, but negative.

  8 % Variable ; this is completely inaccurate, and gives answers like 29, which is blatantly wrong, the largest number it should be is 7.

  how exactly do I do this ?