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• Cannot get libav custom IO to work for jpg image file

  24 octobre 2012, par Bloodwolf

  I am trying to create a custom input stream. However, avformat_open_input
  fails with a random error value. I would appreciate it if someone can tell
  me what is it that I am doing wrong. Here is the simplified code.

  Thank you in advance for your help.

  #define BUFSIZE (4 * 1024)
  
  
  
  static int ReadPacket(void* opaque, uint8_t* buf, int bufsize) 
  
  {
  
      FILE* file = (FILE*) opaque;
  
  
  
      int len = fread(buf, 1, bufsize, file);
  
      return len;
  
  }
  
  
  
  
  
  int main(int argc, char* argv[]) 
  
  {
  
  
  
      av_register_all();
  
      // av_log_set_level(AV_LOG_DEBUG);
  
  
  
      const char* fileName = "/home/alan/sample.jpg";
  
      FILE* file = fopen(fileName, "rb");
  
  
  
      unsigned char* buffer = (unsigned char*) av_malloc(BUFSIZE);
  
  
  
      AVIOContext* avContext = avio_alloc_context(buffer, BUFSIZE, 1, file,ReadPacket, NULL, NULL);
  
  
  
      AVFormatContext* pFormatCtx = avformat_alloc_context();
  
      pFormatCtx->pb = avContext;
  
  
  
      int val = avformat_open_input(&pFormatCtx, fileName, NULL, NULL);
  
      if (val != 0) 
  
      {
  
          printf("Open input failed. Err: %d\n", val);
  
          pFormatCtx = 0; // it is already freed
  
          av_free(avContext);
  
          av_free(buffer);
  
          fclose(file);
  
          return -1;
  
      }
  
  }

  But if I replace the fileName by "/home/alan/demo.avi", it works..

• Building FFmpeg for Android

  13 juin 2013, par varevarao

  I've spent almost a week on this now, trying to get FFmpeg "Angel"/"Happiness" to build for Android.
  I've tried build scripts from all over the internet to no avail. I got closest was using this. As the author himself says the script doesn't work for newer versions of FFmpeg due to this bug, which has been dismissed on that ticket saying "I found a Makefile that does it." This was dis-heartening, being the only post on all of the vast Google world that was anywhere close to my problem.
  So, question time :

  Is there a way to get around the above bug ? I'm trying to use the newest ffmpeg API, and "Love" is just giving me "undefined reference" errors while trying to use av_encode_video2(), and av_free_frame(). The code I was working on the lines of is at the ffmpeg git repo, under /doc/examples/decoding_encoding.c (the function starting on line 338).

  Update : So they've done away with codec_names.sh in "Angel". Sorry didn't notice that before, but the problem persists in a different avatar now. With every build attempt the compiler throws a certain

  start ndk-building...
  
  /home/<user>/android-ndk/build/core/build-binary.mk:41: *** target file `clean&#39; has both : and :: entries.  Stop.
  
  </user>

  Say whatnow !?

• OpenCV Multi-camera handling issue

  19 janvier 2013, par user1797582

  1) I get this errors while handling two logitech c310 cameras with OpenCV(updated Kubuntu Linux)

  VIDIOC_STREAMON : No space left on device

  Whole error log is as below

  **IDIOC_QUERYMENU: Invalid argument
  
  VIDIOC_QUERYMENU: Invalid argument**
  
  VIDIOC_QUERYMENU: Invalid argument
  
  VIDIOC_QUERYMENU: Invalid argument
  
  VIDIOC_QUERYMENU: Invalid argument
  
  VIDIOC_QUERYMENU: Invalid argument
  
  VIDIOC_QUERYMENU: Invalid argument
  
  **libv4l2: error turning on stream: No space left on device**
  
  **VIDIOC_STREAMON: No space left on device**
  
  OpenCV Error: Bad flag (parameter or structure field) (Unrecognized or unsupported array type) in cvGetMat, file /home/rjdp/Computer_Vision/0_Installers/OpenCV-2.4.2/modules/core/src/array.cpp, line 2482
  
  terminate called after throwing an instance of 'cv::Exception'
  
    what():  /home/rjdp/Computer_Vision/0_Installers/OpenCV-2.4.2/modules/core/src/array.cpp:2482: error: (-206) Unrecognized or unsupported array type in function cvGetMat

  2) It happens only when Handling two cameras, Even at default low res 640x480. I still tried to lower resolution in code to 320x240 which also did not work.

  3) I searched in lot of other posts here & on other sites. Which told me there is not enough USB cam bandwidth available. So I tried to plug one cam in front USB & one in the back side which also failed :(

  My Question is :

  Is it possible to solve this issue of bandwith/memory & run two or
  more cameras together on opencv 2.4.2 ?? OpenCV uses ffmpeg to handle I/O so can i tell my camera hardware with some ffmpeg command to take input stream with compressed MPEG mode instead of bandwidth consuming normal mode.

  CODE IS AS BELOW :

  #include "opencv2/opencv.hpp"
  
  #include 
  
  using namespace cv;
  
  
  
  int main(int, char**)
  
  {
  
      VideoCapture cap01(0); // open the default camera
  
      cap01.set(CV_CAP_PROP_FRAME_WIDTH,320);
  
      cap01.set(CV_CAP_PROP_FRAME_HEIGHT,240);
  
      //sleep(1);
  
      if(!cap01.isOpened())  // check if we succeeded
  
          return -1;
  
      namedWindow("Camera01",1);
  
  
  
      VideoCapture cap02(1); // open the default camera
  
      cap02.set(CV_CAP_PROP_FRAME_WIDTH,320);
  
      cap02.set(CV_CAP_PROP_FRAME_HEIGHT,240);
  
     if(!cap02.isOpened())  // check if we succeeded
  
          return -1;
  
      namedWindow("Camera02",1);
  
  
  
      for(;;)
  
      {
  
          Mat frame, frame_1;
  
          //Mat frame02;
  
          cap02 >> frame;
  
          imshow("Camera01", frame);
  
          if(waitKey(30) >= 0) break;
  
          Mat frame_1;
  
          cap02 >> frame_1; 
  
          imshow("Camera02", frame_1);
  
          if(waitKey(30) >= 0) break;
  
      }
  
  
  
      return 0;
  
  }