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• OpenCV's VideoCapture::open Video Source Dialog

  13 novembre 2015, par swtdrgn

  In my current project, when I call VideoCapture::open(camera device index) and the camera is in used by another program, it shows a Video Source dialog and returns true when I select a device that is already in use.

  However, in my [previous] experiment project, when I called VideoCapture::open(camera device index), it doesn’t show this dialog.

  I want to know what is causing the Video Source dialog to show and the program to behave differently from the experimental project.

  This is the source code to the experiment project :

  int main (int argc, char *argv[])
  
  {
  
  
  
      //vars
  
      time_duration td, td1;
  
      ptime nextFrameTimestamp, currentFrameTimestamp, initialLoopTimestamp, finalLoopTimestamp;
  
      int delayFound = 0;
  
      int totalDelay= 0;
  
  
  
      // initialize capture on default source
  
      VideoCapture capture;
  
      std::cout << "capture.open(0): " << capture.open(0) << std::endl;
  
      std::cout << "NOOO" << std::endl;
  
      namedWindow("video", 1);
  
  
  
      // set framerate to record and capture at
  
      int framerate = 15;
  
  
  
      // Get the properties from the camera
  
      double width = capture.get(CV_CAP_PROP_FRAME_WIDTH);
  
      double height = capture.get(CV_CAP_PROP_FRAME_HEIGHT);
  
  
  
      // print camera frame size
  
      //cout << "Camera properties\n";
  
      //cout << "width = " << width << endl <<"height = "<< height << endl;
  
  
  
      // Create a matrix to keep the retrieved frame
  
      Mat frame;
  
  
  
      // Create the video writer
  
      VideoWriter video("capture.avi",0, framerate, cvSize((int)width,(int)height) );
  
  
  
      // initialize initial timestamps
  
      nextFrameTimestamp = microsec_clock::local_time();
  
      currentFrameTimestamp = nextFrameTimestamp;
  
      td = (currentFrameTimestamp - nextFrameTimestamp);
  
  
  
      // start thread to begin capture and populate Mat frame
  
      boost::thread captureThread(captureFunc, &frame, &capture);
  
      // loop infinitely
  
      for(bool q=true;q;)
  
      {
  
          if(frame.empty()){continue;}
  
          //if(cvWaitKey( 5 ) == 'q'){ q=false; }
  
          // wait for X microseconds until 1second/framerate time has passed after previous frame write
  
          while(td.total_microseconds() < 1000000/framerate){
  
              //determine current elapsed time
  
              currentFrameTimestamp = microsec_clock::local_time();
  
              td = (currentFrameTimestamp - nextFrameTimestamp);
  
              if(cvWaitKey( 5 ) == 'q'){
  
                  std::cout << "B" << std::endl;
  
                  q=false;
  
                  boost::posix_time::time_duration timeout = boost::posix_time::milliseconds(0);
  
                  captureThread.timed_join(timeout);
  
                  break;
  
              }
  
          }
  
  
  
          // determine time at start of write
  
          initialLoopTimestamp = microsec_clock::local_time();
  
  
  
          // Save frame to video
  
          video << frame;
  
          imshow("video", frame);
  
  
  
          //write previous and current frame timestamp to console
  
          cout << nextFrameTimestamp << " " << currentFrameTimestamp << " ";
  
  
  
          // add 1second/framerate time for next loop pause
  
          nextFrameTimestamp = nextFrameTimestamp + microsec(1000000/framerate);
  
  
  
          // reset time_duration so while loop engages
  
          td = (currentFrameTimestamp - nextFrameTimestamp);
  
  
  
          //determine and print out delay in ms, should be less than 1000/FPS
  
          //occasionally, if delay is larger than said value, correction will occur
  
          //if delay is consistently larger than said value, then CPU is not powerful
  
          // enough to capture/decompress/record/compress that fast.
  
          finalLoopTimestamp = microsec_clock::local_time();
  
          td1 = (finalLoopTimestamp - initialLoopTimestamp);
  
          delayFound = td1.total_milliseconds();
  
          cout << delayFound << endl;
  
  
  
          //output will be in following format
  
          //[TIMESTAMP OF PREVIOUS FRAME] [TIMESTAMP OF NEW FRAME] [TIME DELAY OF WRITING]
  
          if(!q || cvWaitKey( 5 ) == 'q'){
  
              std::cout << "C" << std::endl;
  
              q=false;
  
              boost::posix_time::time_duration timeout = boost::posix_time::milliseconds(0);
  
              captureThread.timed_join(timeout);
  
              break;
  
          }
  
      }
  
  
  
      // Exit
  
      return 0;
  
  }

  

• FFmpeg encoding produces slightly incompatible MKV/MP4 container

  11 juin 2018, par james2048

  I’ve been using the FFmpeg libraries to read and write media files using the C API.

  So far, reading seems to be pretty straightforward. I am able to read frames which I can then process, convert to RGB, process, and then convert back to YUV420 to be encoded.

  The encoded files play back with VLC media player fine, and Windows Media Player if I have a codec pack installed. However, they do behave strangely : the stock Windows 10 player won’t play them, same for Adobe Premiere. Also thumbnailers don’t work on it.
  Basically it seems like nothing other than VLC or FFmpeg itself can play/process the file. I have seen this with both MP4 and MKV, so it is not a format-specific issue.

  The problems go away once you remux the file with FFmpeg, for example "ffmpeg -i input.mkv -c copy output.mkv". Everything can play the file correctly.
  Also, the "remuxing.c" sample from the official samples works as well, with the same library version and compilers that I’m using (Visual Studio 2017, FFmpeg compiled with MinGW). It will fix the file and make it playable in all software.

  I’m not sure what could be causing this. I also don’t understand what the remuxing "fixed". It must be a container issue as the frames aren’t touched by remuxing.
  I have analysed the output MKVs with FFprobe -show_packets. It seems to have budged the packet timestamps a little constant factor, and the output stream now has
  is_avc=true and nal_length_size=4 instead of is_avc=false and nal_length_size=0, but apart from that the files are identical.

  Now here’s the output of FFprobe with the 3 last test packets, stream info and format info for both streams. As you can see, they are identical except for a couple of field. But something in here must have been "fixed" during remuxing to make it work.

  [PACKET]
  
  codec_type=video
  
  stream_index=0
  
  pts=59050
  
  pts_time=59.050000
  
  dts=58890
  
  dts_time=58.890000
  
  duration=1
  
  duration_time=0.001000
  
  convergence_duration=N/A
  
  convergence_duration_time=N/A
  
  size=427
  
  pos=277358
  
  flags=__
  
  [/PACKET]
  
  [PACKET]
  
  codec_type=video
  
  stream_index=0
  
  pts=58970
  
  pts_time=58.970000
  
  dts=58970
  
  dts_time=58.970000
  
  duration=1
  
  duration_time=0.001000
  
  convergence_duration=N/A
  
  convergence_duration_time=N/A
  
  size=205
  
  pos=277792
  
  flags=__
  
  [/PACKET]
  
  [PACKET]
  
  codec_type=video
  
  stream_index=0
  
  pts=59130
  
  pts_time=59.130000
  
  dts=59050
  
  dts_time=59.050000
  
  duration=1
  
  duration_time=0.001000
  
  convergence_duration=N/A
  
  convergence_duration_time=N/A
  
  size=268
  
  pos=278004
  
  flags=__
  
  [/PACKET]
  
  [STREAM]
  
  index=0
  
  codec_name=h264
  
  codec_long_name=H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
  
  profile=Main
  
  codec_type=video
  
  codec_time_base=1/2000
  
  codec_tag_string=[0][0][0][0]
  
  codec_tag=0x0000
  
  width=720
  
  height=576
  
  coded_width=720
  
  coded_height=576
  
  has_b_frames=2
  
  sample_aspect_ratio=N/A
  
  display_aspect_ratio=N/A
  
  pix_fmt=yuv420p
  
  level=50
  
  color_range=unknown
  
  color_space=unknown
  
  color_transfer=unknown
  
  color_primaries=unknown
  
  chroma_location=left
  
  field_order=progressive
  
  timecode=N/A
  
  refs=1
  
  is_avc=false
  
  nal_length_size=0
  
  id=N/A
  
  r_frame_rate=299/12
  
  avg_frame_rate=1000/1
  
  time_base=1/1000
  
  start_pts=0
  
  start_time=0.000000
  
  duration_ts=N/A
  
  duration=N/A
  
  bit_rate=N/A
  
  max_bit_rate=N/A
  
  bits_per_raw_sample=8
  
  nb_frames=N/A
  
  nb_read_frames=N/A
  
  nb_read_packets=737
  
  DISPOSITION:default=1
  
  DISPOSITION:dub=0
  
  DISPOSITION:original=0
  
  DISPOSITION:comment=0
  
  DISPOSITION:lyrics=0
  
  DISPOSITION:karaoke=0
  
  DISPOSITION:forced=0
  
  DISPOSITION:hearing_impaired=0
  
  DISPOSITION:visual_impaired=0
  
  DISPOSITION:clean_effects=0
  
  DISPOSITION:attached_pic=0
  
  DISPOSITION:timed_thumbnails=0
  
  TAG:DURATION=00:00:59.211000000
  
  [/STREAM]
  
  [FORMAT]
  
  filename=testEncLeft.mkv
  
  nb_streams=1
  
  nb_programs=0
  
  format_name=matroska,webm
  
  format_long_name=Matroska / WebM
  
  start_time=0.000000
  
  duration=59.211000
  
  size=278349
  
  bit_rate=37607
  
  probe_score=100
  
  TAG:COMMENT=Slickline Player Export
  
  TAG:ENCODER=Lavf57.83.100
  
  [/FORMAT]

  And the info after remuxing, which works :

  [PACKET]
  
  codec_type=video
  
  stream_index=0
  
  pts=59050
  
  pts_time=59.050000
  
  dts=58890
  
  dts_time=58.890000
  
  duration=1
  
  duration_time=0.001000
  
  convergence_duration=N/A
  
  convergence_duration_time=N/A
  
  size=427
  
  pos=277418
  
  flags=__
  
  [/PACKET]
  
  [PACKET]
  
  codec_type=video
  
  stream_index=0
  
  pts=58970
  
  pts_time=58.970000
  
  dts=58970
  
  dts_time=58.970000
  
  duration=1
  
  duration_time=0.001000
  
  convergence_duration=N/A
  
  convergence_duration_time=N/A
  
  size=205
  
  pos=277852
  
  flags=__
  
  [/PACKET]
  
  [PACKET]
  
  codec_type=video
  
  stream_index=0
  
  pts=59130
  
  pts_time=59.130000
  
  dts=59050
  
  dts_time=59.050000
  
  duration=1
  
  duration_time=0.001000
  
  convergence_duration=N/A
  
  convergence_duration_time=N/A
  
  size=268
  
  pos=278064
  
  flags=__
  
  [/PACKET]
  
  [STREAM]
  
  index=0
  
  codec_name=h264
  
  codec_long_name=H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
  
  profile=Main
  
  codec_type=video
  
  codec_time_base=1/2000
  
  codec_tag_string=[0][0][0][0]
  
  codec_tag=0x0000
  
  width=720
  
  height=576
  
  coded_width=720
  
  coded_height=576
  
  has_b_frames=2
  
  sample_aspect_ratio=N/A
  
  display_aspect_ratio=N/A
  
  pix_fmt=yuv420p
  
  level=50
  
  color_range=unknown
  
  color_space=unknown
  
  color_transfer=unknown
  
  color_primaries=unknown
  
  chroma_location=left
  
  field_order=progressive
  
  timecode=N/A
  
  refs=1
  
  is_avc=true
  
  nal_length_size=4
  
  id=N/A
  
  r_frame_rate=299/12
  
  avg_frame_rate=1000/1
  
  time_base=1/1000
  
  start_pts=0
  
  start_time=0.000000
  
  duration_ts=N/A
  
  duration=N/A
  
  bit_rate=N/A
  
  max_bit_rate=N/A
  
  bits_per_raw_sample=8
  
  nb_frames=N/A
  
  nb_read_frames=N/A
  
  nb_read_packets=737
  
  DISPOSITION:default=1
  
  DISPOSITION:dub=0
  
  DISPOSITION:original=0
  
  DISPOSITION:comment=0
  
  DISPOSITION:lyrics=0
  
  DISPOSITION:karaoke=0
  
  DISPOSITION:forced=0
  
  DISPOSITION:hearing_impaired=0
  
  DISPOSITION:visual_impaired=0
  
  DISPOSITION:clean_effects=0
  
  DISPOSITION:attached_pic=0
  
  DISPOSITION:timed_thumbnails=0
  
  TAG:DURATION=00:00:59.212000000
  
  [/STREAM]
  
  [FORMAT]
  
  filename=fixedLeft.mkv
  
  nb_streams=1
  
  nb_programs=0
  
  format_name=matroska,webm
  
  format_long_name=Matroska / WebM
  
  start_time=0.000000
  
  duration=59.212000
  
  size=278409
  
  bit_rate=37615
  
  probe_score=100
  
  TAG:COMMENT=Slickline Player Export
  
  TAG:ENCODER=Lavf58.12.100
  
  [/FORMAT]

  Here is how I’m setting up the output context, for reference : it’s pretty standard, following the sample code.

  int ret;
  
  
  
  avformat_alloc_output_context2(&outputFormatCtx, nullptr, nullptr, outFilePath.c_str());
  
  
  
  av_dict_set(&outputFormatCtx->metadata, "comment", "FFmpeg Export", 0);
  
  
  
  if (!outputFormatCtx)
  
  {
  
      LOG_AND_THROW("Could not allocate output context");
  
  }
  
  
  
  outputVideoStream = avformat_new_stream(outputFormatCtx, nullptr);
  
  outputVideoStream->time_base = AVRational{ 1, AV_TIME_BASE }; // Stream timebase will be used by codec
  
  
  
  if (!outputVideoStream)
  
  {
  
      LOG_AND_THROW("Failed allocating output stream");
  
  }
  
  
  
  // defaults to "libx264"
  
  AVCodec *outCodec = avcodec_find_encoder_by_name(selectedCodecName.c_str());
  
  
  
  if (!outCodec)
  
  {
  
      LOG_AND_THROW("Failed finding output codec");
  
  }
  
  
  
  AVDictionary *opts = nullptr;
  
  
  
  if (selectedCodecName == "libx264")
  
  {
  
      opts = getX264CodecOptions();
  
  }
  
  
  
  encoderCtx = avcodec_alloc_context3(outCodec);
  
  
  
  if (!encoderCtx)
  
  {
  
      LOG_AND_THROW("Failed to allocate the encoder context");
  
  }
  
  
  
  encoderCtx->width = width;
  
  encoderCtx->height = height;
  
  encoderCtx->pix_fmt = AV_PIX_FMT_YUV420P;
  
  // time base for the frames we will provide to the encoder
  
  encoderCtx->time_base = AVRational{ 1, AV_TIME_BASE };
  
  // convert framerate from double to rational
  
  encoderCtx->framerate = AVRational{ (int)(frameRate * AV_TIME_BASE), AV_TIME_BASE};
  
  
  
  // Match encoderCtx time base for the stream
  
  outputVideoStream->time_base = encoderCtx->time_base;
  
  
  
  ret = avcodec_open2(encoderCtx, outCodec, &opts);
  
  
  
  if (ret < 0)
  
  {
  
      LOG_AND_THROW_PARAM("Cannot open video encoder for stream: %d", ret);
  
  }
  
  
  
  // Fill in some params for MP4 stream, details about encoder
  
  ret = avcodec_parameters_from_context(outputVideoStream->codecpar, encoderCtx);
  
  
  
  if (ret < 0)
  
  {
  
      LOG_AND_THROW_PARAM("Failed to copy encoder parameters to output stream: %d", ret);
  
  }
  
  
  
  if (outputFormatCtx->oformat->flags & AVFMT_GLOBALHEADER)
  
  {
  
      encoderCtx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
  }
  
  
  
  av_dump_format(outputFormatCtx, 0, filePath.c_str(), 1);
  
  
  
  // End of encoder settings, setting up MP4
  
  if (!(outputFormatCtx->oformat->flags & AVFMT_NOFILE))
  
  {
  
      ret = avio_open(&outputFormatCtx->pb, outFilePath.c_str(), AVIO_FLAG_WRITE);
  
  
  
      if (ret < 0)
  
      {
  
          LOG_AND_THROW_PARAMSTR("Could not open output file '%s'", outFilePath.c_str());
  
      }
  
  }
  
  
  
  ret = avformat_write_header(outputFormatCtx, nullptr);
  
  
  
  if (ret < 0)
  
  {
  
      LOG_AND_THROW_PARAM("Error occurred when opening output file for writing: %d", ret);
  
  }

  Can anyone help me figure out why the container is not playing properly ?

  Thanks in advance.

  -James

• Extracting audio from video command fails for some videos

  16 juin 2018, par Java Android

  I am using below FFmpeg command for extracting audio from video-

  String[] complexCommand = new String[]"-y","-ss", "" +
  startMs / 1000, "-t", "" + (endMs - startMs) / 1000, "-i",
  inputFileAbsolutePath, "-vn", "-ar", "44100", "-ac", "2", "-b:a",
  "256k", "-f", "mp3", outputFileAbsolutePath ;

  It works fine in my device but through analytics I came to know that its failing for many users or for many videos.I failed to understand whats wrong with the command and why its failing many times ?