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• cvCaptureFromFile always returns NULL, Visual Studio 2005

  14 septembre 2012, par user1671173

  I've got a problem with the cvCaptureFromFile function. It always returns NULL. I've done some research on the internet and I've added PATH to ffmpeg's "bin" directory.
  But it's still the same. So I've tried to open the desired file with ffplay.exe. It returns an error which says "Invalid data found when processing an input". It is a "mjpg" file, which should be played with ffmpeg. Then I tried the same with some "mpg" file.
  Now the message is "no such file or directory" which is not true, because the file is in the place. What else should I do ?
  The files all right with Media-Player and VLC player.
  Please help !

• capture.isOpened() returns false in python [closed]

  24 décembre 2019, par Elnaz Yousefi

  I tried to read a video (.avi file) by cv2.VideoCapture in Python, but capture.isOpened() returns false.
  when I execute python in cmd, it returns "Python 3.7.2". Also, when I use "pip install opencv-python" in command line, OpenCV was successfully installed.
  By the way, I noticed that the version of opencv which is installed is 4.1.2 and the ffmpeg file is named "opencv_videoio_ffmpeg412".
  Is everything right ? so what’s the problem ?

• SDL and iOS main() methods conflict

  15 novembre 2016, par 谢小进

  I have learnt that SDL project need main() method to run loop, code like this :

  #include "SDL.h"
  
  
  
  int main(int argc, char *argv[])
  
  {
  
      if (SDL_Init(SDL_INIT_VIDEO) < 0) {
  
          printf("%s\n", SDL_GetError());
  
      }
  
  
  
      SDL_Window *window = SDL_CreateWindow(NULL, 0, 0, 320, 640, SDL_WINDOW_OPENGL | SDL_WINDOW_FULLSCREEN);
  
      SDL_Renderer *renderer = SDL_CreateRenderer(window, 0, 0);
  
  
  
      SDL_Surface *bmp_surface = SDL_LoadBMP("space.bmp");
  
      SDL_Texture *space = SDL_CreateTextureFromSurface(renderer, bmp_surface);
  
      SDL_FreeSurface(bmp_surface);
  
  
  
      SDL_RenderCopy(renderer, space, NULL, NULL);
  
      SDL_RenderPresent(renderer);
  
  
  
      int done = 0;
  
      while (!done) {
  
          Uint32 startFrame = SDL_GetTicks();
  
          SDL_Event event;
  
          while (SDL_PollEvent(&event)) {
  
              if (event.type == SDL_QUIT) {
  
                  done = 1;
  
              }
  
          }
  
          Uint32 endFrame = SDL_GetTicks();
  
  
  
          Sint32 delay = MILLESECONDS_PER_FRAME - (endFrame - startFrame);
  
          if (delay < 0) {
  
              delay = 0;
  
          } else if (delay > MILLESECONDS_PER_FRAME) {
  
              delay = MILLESECONDS_PER_FRAME;
  
          }
  
          SDL_Delay(delay);
  
      }
  
  
  
      SDL_DestroyTexture(space);
  
      SDL_Quit();
  
  
  
      return 0;
  
  }

  And iOS project also need main() method, code like this :

  #import <uikit></uikit>UIKit.h>
  
  
  
  #import "AppDelegate.h"
  
  
  
  int main(int argc, char * argv[])
  
  {
  
      @autoreleasepool {
  
          return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
  
      }
  
  }

  Now I need integrate SDL library to an iOS project, but there need two main() methods. How ? If yes, can anybody show some more codes ? Thanks.