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• C++/OpenCV - VideoCapture doesn't work but it worked before with exactly the same code

  5 mars 2015, par Damià Obrador

  I’m trying to write a shot boundary detection algorithm in C++ using OpenCV. After all, I have to say that I have no experience working with OpenCV.

  I have been improving the following code (and I am still in it) during the last two weeks and everything seems the works correctly, not in terms of perfect shot detection, but every line of code did what was expected from it.

  #include <cstdlib>
  
  #include <opencv2></opencv2>opencv.hpp>
  
  #include <opencv2></opencv2>core/core.hpp>
  
  #include <opencv2></opencv2>video/background_segm.hpp>
  
  #include <opencv2></opencv2>highgui/highgui.hpp>
  
  #include <iostream>
  
  #include <opencv2></opencv2>imgproc/imgproc.hpp>
  
  #include 
  
  #include <istream>
  
  #include <fstream>
  
  using namespace cv;
  
  
  
  
  
  
  
  int main(){
  
  
  
      VideoCapture capture("vdevendetta.mp4");
  
      if ( !capture.isOpened() )
  
       {
  
           std::cout &lt;&lt; "Cannot open the video file";
  
           return -1;
  
       }
  
      int numFrames=capture.get(CV_CAP_PROP_FRAME_COUNT);
  
      bool SB_counter=false;
  
      Mat currentFrame;
  
      Mat frame;
  
      Mat fore;
  
      Mat back;
  
      vector<mat> frames;
  
      FileStorage file;
  
      FileStorage file2;
  
      Mat prev_Y;
  
      Mat channels[3];
  
      for(int i=0;i>currentFrame;
  
              frame=currentFrame.clone();
  
              cvtColor(frame,frame,CV_BGR2YUV);
  
              split( frame, channels );
  
              prev_Y=channels[0];
  
              SB_counter=false;
  
          }
  
          else
  
          {
  
              capture>>currentFrame;
  
              frame=currentFrame.clone();
  
              Mat channels[3];
  
              cvtColor(frame,frame,CV_BGR2YUV);
  
              split( frame, channels );
  
              Mat curr_Y=channels[0];
  
              channels[0]=prev_Y;
  
              prev_Y=curr_Y;
  
              merge(channels,3,frame);
  
              cvtColor(frame,frame,CV_Luv2BGR);
  
              cvtColor(frame,frame,CV_BGR2GRAY);
  
              frames.push_back(frame);
  
          }
  
  
  
      }
  
  
  
      vector<double> MAFDs;
  
      vector<double> MAFD;
  
      vector<double> aux;
  
      double min;
  
      double min2;
  
  
  
      for(int j=1;j14)
  
          {
  
              std::cout&lt;&lt;"De"&lt;*
  
      std::ofstream fout("MAFD.txt");
  
      if(fout.is_open()==true)
  
      {
  
        //file opened successfully so we are here
  
        std::cout &lt;&lt; "File Opened successfully!!!. Writing data from array to file" &lt;&lt; std::endl;
  
  
  
          for(int i = 0; MAFD[i] != '\0'; i++)
  
          {
  
          fout &lt;&lt; MAFD[i]; //writing ith character of array in the file
  
          }
  
        std::cout &lt;&lt; "Array data successfully saved into the file test.txt" &lt;&lt; std::endl;
  
      }
  
      else //file could not be opened
  
      {
  
          std::cout &lt;&lt; "File could not be opened." &lt;&lt; std::endl;
  
      }*/
  
      return 0;
  
  }
  
  </double></double></double></mat></fstream></istream></iostream></cstdlib>

  Three days ago I had an strange problem. The line :

  VideoCapture capture("vdevendetta.mp4");

  stopped working. I spent many hours looking for the solution but nothing seems to repair it. After reading everything related with OpenCV, VideoCapture and ffmpeg that I found on internet I decided to reinstall everything taking care of each detail, but it still didn’t work. Finally I solved it changing the line with this other one :

  VideoCapture capture("/home/damia/Documentos/Universitat/ARA/PAEAV/workspace_cpp/SBD/src/vdevendetta.mp4");

  I did not know why this solved it because the video is in the same directory than the program, but I continued working because everything seemed correct.
  Today I had the same problem again on the new line.
  The terminal doesn’t show any error comment (exceptuating "Cannot open the video file", obviously) but the code doesn’t work again.

  I’m using Ubuntu 14.04 LTS, OpenCV 2.4.9 and Eclipse.

  I think if someone test the code it will run correctly, but I would like to know if there is something I have no taking into account.

  Thank you very match.

• Encoding a live stream of bitmaps using FFMPEG

  1er avril 2015, par user3088260

  I’ve got a constant stream of jpeg’s that need to be converted to a video (of any kind).
  The problem is that the stream is virtually infinite and I don’t know any method of creating videos using pictures that doesn’t store the whole file in memory until the stream stops..

  Is there a way that I can feed FFMPEG with bitmaps or jpegs constantly from c# or at least make ffmpeg read images from a folder with +432000 images (on the command line) ?

  Please note that there will be no sound, the images will be low quality, they will come at a rate 5 FPS and this will run on a high-ish end laptop. BTW I can provide code but I assume this is unnecessary at the moment as I am only creating bitmaps and saving them.

• ffmpeg run from shell runs properly, but does not when called from within .NET

  2 juillet 2013, par Bevin

  I'm attempting to use ffmpeg (compiled on Windows with Cygwin) in a C# program, by using the Process class to spawn an ffmpeg instance. However, I've hit a rather odd bug that doesn't make much sense.

  When I run ffmpeg directly from a shell (be it Cygwin's bash, PowerShell, cmd), ffmpeg can properly decode and reencode files without any issues :

  PS C:\audio> ffmpeg -i .\sound1.wav -acodec libvorbis -f ogg abc.ogg
  
  ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  
    built on Apr  8 2013 15:10:40 with gcc 4.5.3 (GCC)
  
    configuration: --disable-encoder=vorbis --enable-libvorbis
  
    libavutil      52. 18.100 / 52. 18.100
  
    libavcodec     54. 92.100 / 54. 92.100
  
    libavformat    54. 63.104 / 54. 63.104
  
    libavdevice    54.  3.103 / 54.  3.103
  
    libavfilter     3. 42.103 /  3. 42.103
  
    libswscale      2.  2.100 /  2.  2.100
  
    libswresample   0. 17.102 /  0. 17.102
  
  [wav @ 0x800538a0] max_analyze_duration 5000000 reached at 5015510 microseconds
  
  Guessed Channel Layout for  Input Stream #0.0 : stereo
  
  Input #0, wav, from '.\sound1.wav':
  
    Metadata:
  
      encoder         : Lavf54.63.104
  
    Duration: 00:00:05.76, bitrate: 1411 kb/s
  
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
  
  Output #0, ogg, to 'abc.ogg':
  
    Metadata:
  
      encoder         : Lavf54.63.104
  
      Stream #0:0: Audio: vorbis, 44100 Hz, stereo, fltp
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (pcm_s16le -> libvorbis)
  
  Press [q] to stop, [?] for help
  
  size=      55kB time=00:00:05.74 bitrate=  78.5kbits/s
  
  video:0kB audio:51kB subtitle:0 global headers:4kB muxing overhead 0.817473%

  The file plays fine, and I can encode to WAV or any other format I like. However, when I call ffmpeg from C# with the following code :

  string tempfile = Path.GetTempFileName();
  
  FileStream tempfilestr = File.OpenWrite(tempfile);
  
  input.CopyTo(tempfilestr);
  
  
  
  ProcessStartInfo pstart = new ProcessStartInfo("ffmpeg", string.Format("-i \"{0}\" -v verbose -y -f wav -", tempfile));
  
  pstart.CreateNoWindow = true;
  
  pstart.ErrorDialog = false;
  
  pstart.RedirectStandardOutput = true;
  
  pstart.RedirectStandardError = true;
  
  pstart.UseShellExecute = false;
  
  
  
  
  
  Process proc = new Process();
  
  proc.StartInfo = pstart;
  
  proc.Start();
  
  StreamReader stdout = proc.StandardOutput;
  
  StreamReader stderr = proc.StandardError;
  
  
  
  outtempfilestr = File.OpenRead(outtempfile);
  
  MemoryStream output = new MemoryStream();
  
  
  
  stdout.BaseStream.CopyTo(output);
  
  
  
  try {
  
      proc.Kill();
  
  }
  
  catch(InvalidOperationException) { }
  
  catch(Win32Exception) { }
  
  
  
  File.Delete(tempfile);
  
  
  
  return output.ToArray();

  This randomly produces errors in the output :

  ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  
    built on Apr  8 2013 15:10:40 with gcc 4.5.3 (GCC)
  
    configuration: --disable-encoder=vorbis --enable-libvorbis
  
    libavutil      52. 18.100 / 52. 18.100
  
    libavcodec     54. 92.100 / 54. 92.100
  
    libavformat    54. 63.104 / 54. 63.104
  
    libavdevice    54.  3.103 / 54.  3.103
  
    libavfilter     3. 42.103 /  3. 42.103
  
    libswscale      2.  2.100 /  2.  2.100
  
    libswresample   0. 17.102 /  0. 17.102
  
  [wav @ 0x80053860] parser not found for codec pcm_s16le, packets or times may be invalid.
  
      Last message repeated 1 times
  
  [wav @ 0x80053860] max_analyze_duration 5000000 reached at 5015510 microseconds
  
  Guessed Channel Layout for  Input Stream #0.0 : stereo
  
  Input #0, wav, from 'C:\Users\Bevin\AppData\Local\Temp\tmp1CCE.tmp':
  
    Duration: 00:00:05.20, bitrate: 1411 kb/s
  
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
  
  [graph 0 input from stream 0:0 @ 0x8011f320] tb:1/44100 samplefmt:s16 samplerate:44100 chlayout:0x3
  
  Output #0, wav, to 'pipe:':
  
    Metadata:
  
      ISFT            : Lavf54.63.104
  
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, stereo, s16, 1411 kb/s
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)
  
  Press [q] to stop, [?] for help
  
  Multiple frames in a packet from stream 0
  
  [pcm_s16le @ 0x8005c160] Invalid PCM packet, data has size 3 but at least a size of 4 was expected
  
  Error while decoding stream #0:0: Invalid data found when processing input
  
  No more output streams to write to, finishing.
  
  size=     896kB time=00:00:05.20 bitrate=1411.3kbits/s    
  
  video:0kB audio:896kB subtitle:0 global headers:0kB muxing overhead 0.008719%

  Note that these errors don't always occur. Sometimes they happen for certain files, sometimes they don't. I've tried various combinations of stream redirects and temp files, none of them work. I've also verified the integrity of the temp files, and it all checks out. I've even extracted the temp file before it was deleted, and decoded it in shell without a hitch.

  Any ideas ?

  Edit : I've tried running ffmpeg from a shell script that's run through C#. It gives the same issues. Compiling ffmpeg via MinGW gives the same issue as well.