Showing a video using two textures SDL2 - c++

Question

I need to build an interface where on the left side of the screen shows part of one streaming video and the right side the other part. Something like this https://www.youtube.com/watch?v=fSPXpdVzamo
The video streaming is saved on a memory buffer that is being loaded on a texture. My question is how to render just the half of the texture, I've bee trying using SDL_Rect but nothing happens.
This is the relevant part of my code:
SDL_UpdateTexture(texture, NULL, buffer_start, fmt.fmt.pix.width * 2);
SDL_RenderClear(renderer);
SDL_RenderCopy(renderer, texture, NULL, NULL);
SDL_RenderPresent(renderer);
If I try something like this, it doesn't work:
SDL_UpdateTexture(texture, NULL, buffer_start, fmt.fmt.pix.width * 2);
SDL_Rect someRect;
someRect.x = 0;
someRect.y = 0;
someRect.w = 1500;
someRect.h = 3000;
SDL_RenderClear(renderer);
SDL_RenderCopy(renderer, texture, NULL, &someRect);
SDL_RenderPresent(renderer);
Any advice would be great!

Answer 1

Without you posting a MCVE is hard to know where you went wrong. My guess is your x position is wrong. Here is an example where I show how to draw 2 images in the fashion of your video.
Green image: https://i.imgur.com/yaOG8Ng.png
Red image: https://i.imgur.com/faKKShU.png
#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <iostream>
#define HEIGHT 600
#define WIDTH 800
using namespace std;
int main() {
SDL_Init(SDL_INIT_VIDEO);
SDL_Window *window = SDL_CreateWindow("Red Green", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, WIDTH, HEIGHT, SDL_WINDOW_SHOWN);
SDL_Renderer *renderer = SDL_CreateRenderer(window, 0, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
bool quit = false;
SDL_Event event;
SDL_Texture *green_part = IMG_LoadTexture(renderer, "Green400x600.png");
SDL_Texture *red_part = IMG_LoadTexture(renderer, "Red400x600.png");
while (!quit) {
while (SDL_PollEvent(&event)) {
if (event.type == SDL_QUIT) {
quit = true;
}
}
SDL_RenderClear(renderer);
SDL_Rect copy_rect{0, 0, 400, 600};
SDL_RenderCopy(renderer, green_part, nullptr, &copy_rect);
// We now draw from half the screen onward x position = WIDTH / 2.
copy_rect.x = 400;
SDL_RenderCopy(renderer, red_part, nullptr, &copy_rect);
SDL_RenderPresent(renderer);
}
SDL_DestroyWindow(window);
SDL_DestroyRenderer(renderer);
SDL_Quit();
return 0;
}