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• the ffmpeg library cannot open camera on android

  27 septembre 2013, par GilGaMesh

  I have successfully ported ffmpeg 2.0.1 lib to android. The code to open camera is very simple :

  AVFormatContext *fmt_ctx = NULL;
  
  AVInputFormat *input_fmt;
  
  
  
  input_fmt = av_find_input_format("video4linux2"); 
  
  if (input_fmt == NULL)
  
      return -1；
  
  
  
  char f_name[] = "/dev/video0";
  
  if ((ret = avformat_open_input(&fmt_ctx, f_name, input_fmt, NULL)) < 0)        // stuck here
  
  {
  
      LOG_D("can not open camera, ret = %d", ret);
  
      return ret;
  
  }

  the strange thing is the ret value is always negative with the following logcat output by av_log :

  09-26 15:27:48.901: E/Codec-FFMpeg(17716): ioctl(VIDIOC_G_PARM): Invalid argument

  I change the f_name to /dev/video1 and /dev/video2 (these files indeed exist on my tablet, and my tablet has 2 cameras) and the problems remains.
  Do i forget anything before calling avformat_open_input() ? Thank you !

• How to open webcam in opencv2.4.6.1 on ubuntu12.04 ?

  20 septembre 2013, par user2079542

  I am using opencv2.4.6.1 on Ubuntu 12.04 LTS. I am new to opencv and have been trying to understand the sample programs in the opencv docs. I am trying to work on a project which takes a picture from a USB webcam (Kinamax Night Vision Camera) and do some image processing on it. I came across a sample code that is shown below :

  #include "cv.h" 
  
  #include "highgui.h" 
  
  #include   
  
  // A Simple Camera Capture Framework 
  
  int main() 
  
  {
  
  CvCapture* capture = cvCaptureFromCAM( CV_CAP_ANY );
  
  if ( !capture ) {
  
   fprintf( stderr, "ERROR: capture is NULL \n" );
  
   getchar();
  
   return -1;
  
  }
  
  // Create a window in which the captured images will be presented
  
  cvNamedWindow( "mywindow", CV_WINDOW_AUTOSIZE );
  
  // Show the image captured from the camera in the window and repeat
  
  while ( 1 ) {
  
   // Get one frame
  
   IplImage* frame = cvQueryFrame( capture );
  
   if ( !frame ) {
  
     fprintf( stderr, "ERROR: frame is null...\n" );
  
     getchar();
  
     break;
  
   }
  
   cvShowImage( "mywindow", frame );
  
   // Do not release the frame!
  
   //If ESC key pressed, Key=0x10001B under OpenCV 0.9.7(linux version),
  
   //remove higher bits using AND operator
  
   if ( (cvWaitKey(10) & 255) == 27 ) break;
  
  }
  
  // Release the capture device housekeeping
  
  cvReleaseCapture( &capture );
  
  cvDestroyWindow( "mywindow" );
  
  return 0;
  
  }

  On compiling using :

  g++ trycam.c -o trycam `--cflags --libs opencv`

  It gives no errors.
  When I try to run it using : ./trycam Nothing shows up ! Literally Nothing.

  On searching google and some other posts in the stackoverflow community, I tried updating the libraries and install other dependencies like ffmpeg,GTK, Gstreamer,etc. I understand that the webcam I have connected via USB is not supported as per the list of webcams supported by linux opencv in the link here. Even my default webcam that is in my HP Pavilion dv6000 is not opening.

  Is there a way I could get around this ? Kindly help me out.

• Solving `libavcodec-ffmpeg.so.56 : cannot open shared object file : No such file or directory` on Ubuntu 17.10

  13 février 2018, par Ionică Bizău

  When running a specific script, I’m getting the following error :

  libavcodec-ffmpeg.so.56: cannot open shared object file: No such file or directory

  I think it’s because ffmpeg 56 is not installed, because I recently upgraded from Ubuntu 16.04 to 17.10.

  How can I get this shared object file ?