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• OpenCV and GoPro - empty frames in VideoCapture stream

  19 mai 2014, par Novatar

  I have a GoPro Hero 3+ (Black) which is connected to a video capture card (AverMedia Game Broadcaster HD). I simply want to get the video stream in OpenCV. With a Logitech Webcam there are no problems. The used code is below.

  VideoCapture cap;
  
  cap.open(0);
  
  
  
  waitKey(300);
  
  
  
  //cap.set(CV_CAP_PROP_FRAME_WIDTH, 1280);
  
  //cap.set(CV_CAP_PROP_FRAME_HEIGHT, 720);
  
  
  
  if (cap.isOpened()){
  
      cout << "Cam identified" << endl;
  
  }
  
  
  
  namedWindow("dst", 1);
  
  
  
  while (1){
  
  
  
  Mat frame;
  
  
  
  if (!cap.read(frame)) {
  
      std::cout << "Unable to read frame from video stream" << std::endl;
  
      continue;
  
  }
  
  
  
  imshow("dst", frame);
  
  
  
  [...]
  
  
  
  }

  With the GoPro the following happens : OpenCV is able to open the VideoCapture ("Cam identified") but can’t read any frames (just a gray screen and the output : "Unable to read frame from video stream"). I also checked this with frame.empty() ;.

  I know that the video capture card works correct because Unity opens a WebCamTexture with the GoPro stream without any issues. I read about codec problems in OpenCv and so I already tried to compile OpenCV with FFMPEG support. Now the recorded MP4-Videos of the GoPro can be displayed but the stream still doesn’t work.

  I use OpenCV 2.48, Windows 7 and Visual Studio 2013.

  ---

  EDIT : Here is the code of libVLC solution :

  struct ctx
  
  {
  
  uint8_t* pixeldata;
  
  std::mutex imagemutex;
  
  };
  
  
  
  static void display(void *data, void *id);
  
  static void unlock(void *data, void *id, void *const *p_pixels);
  
  static void *lock(void *data, void **p_pixels);
  
  
  
  struct ctx ctx;
  
  
  
  libvlc_instance_t *inst;
  
  libvlc_media_player_t *mp;
  
  libvlc_media_t *m;
  
  
  
  int main(int argc, char* argv[])
  
  {
  
      ctx.pixeldata = new uint8_t[1280 * 720 * 3];
  
  
  
      char const *vlc_argv[] =
  
      {
  
          "-vvv",
  
          "--no-audio", /* skip any audio track */
  
          "--no-xlib", /* tell VLC to not use Xlib */
  
      };
  
  
  
      int vlc_argc = sizeof(vlc_argv) / sizeof(*vlc_argv);
  
      inst = libvlc_new(vlc_argc, vlc_argv);
  
  
  
      const char *options[] =
  
      {
  
          ":dshow-vdev=AVerMedia HD Capture",
  
          ":dshow-adev=none",
  
          //":dshow-size=1280x720",
  
          ":dshow-fps=24",
  
          ":dshow-chroma=YUY2",
  
          ":dshow-video-input=1",
  
          ":dshow-video-output=1",
  
          ":dshow-aspect-ratio=16\:9",
  
          ":live-caching=80",
  
          NULL
  
      };
  
  
  
      m = libvlc_media_new_location(inst, "dshow://");
  
      for (const char **opt = options; *opt; opt++)
  
          libvlc_media_add_option(m, *opt);
  
  
  
      mp = libvlc_media_player_new_from_media(m);
  
      libvlc_media_release(m);
  
      libvlc_video_set_callbacks(mp, lock, unlock, display, &ctx);
  
      libvlc_video_set_format(mp, "RV24", 1280, 720, 1280 * 3);
  
      libvlc_media_player_play(mp);
  
  
  
      namedWindow("all", 1);
  
  
  
      Mat frame(720, 1280, CV_8UC3);
  
  
  
      while (1){
  
  
  
          ctx.imagemutex.lock();
  
          memcpy(gesamt.data, ctx.pixeldata, 1280 * 720 * sizeof(uint8_t) * 3);
  
          ctx.imagemutex.unlock();
  
  
  
          imshow("all", gesamt);
  
  
  
          if (waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
  
          {
  
              cout << "esc key is pressed by user" << endl;
  
              break;
  
          }
  
  
  
      }
  
  
  
      libvlc_media_player_stop(mp);
  
      libvlc_media_player_release(mp);
  
      libvlc_release(inst);
  
      delete[] ctx.pixeldata;
  
  
  
      return 0;
  
  }
  
  
  
  void display(void *data, void *id){
  
      (void)data;
  
      assert(id == NULL);
  
  }
  
  
  
  void unlock(void *data, void *id, void *const *p_pixels){
  
      struct ctx *ctx = (struct ctx*)data;
  
      ctx->imagemutex.unlock();
  
      assert(id == NULL);
  
  }
  
  
  
  void *lock(void *data, void **p_pixels){
  
      struct ctx *ctx = (struct ctx*)data;
  
      ctx->imagemutex.lock();
  
      *p_pixels = ctx->pixeldata;
  
      return NULL;
  
  }

• ffmpeg merge video and audio result empty file [on hold]

  10 février 2015, par ahmed-ibrahem

  I have empty file when try to merge mp4 & mp3 to mp4

  Code : ( not working )

  ffmpeg -i video.mp4 -i audio.mp3 output.mp4

  Code : ( working )

  ffmpeg -i video.mp4 -i audio.mp3 -vcodec copy -acodec copy output.mp4

  but using above working command instead of mp3 when i try wav result empty file only

  Note : This is where i got the <a href="https://github.com/JayH5/android-ffmpeg-cmdline" rel="nofollow">ffmpeg for android</a>

  Can any one help me to make it merge the audio.wav with the video.mp4 ?

• An ISO ripped from a DVD-Video is empty but still plays in Apple DVD-Player ?

  7 avril 2015, par IAmDamoSuzuki

  I’ve run across a number of DVDs that seem to contain no visible data. The ISOs that I rip from them (using ddrescue) contain no VIDEO_TS folders, or any folders at all. However, if I use df on the mounted filesystem it claims to have a size.

  Even stranger however, is that the Apple DVD-Player and MPEG-Streamclip will still open and play the DVD. I’m unable to process the ISOs using ffmpeg because terminal can’t see any files !

  Has anybody experienced something like this before ?