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• Segmentation fault with avcodec_encode_video2() while encoding H.264

  16 juillet 2015, par Baris Demiray

  I’m trying to convert a cv::Mat to an AVFrame to encode it then in H.264 and wanted to start from a simple example, as I’m a newbie in both. So I first read in a JPEG file, and then do the pixel format conversion with sws_scale() from AV_PIX_FMT_BGR24 to AV_PIX_FMT_YUV420P keeping the dimensions the same, and it all goes fine until I call avcodec_encode_video2().

  I read quite a few discussions regarding an AVFrame allocation and the question segmetation fault while avcodec_encode_video2 seemed like a match but I just can’t see what I’m missing or getting wrong.

  Here is the minimal code that you can reproduce the crash, it should be compiled with,

  g++ -o OpenCV2FFmpeg OpenCV2FFmpeg.cpp -lopencv_imgproc -lopencv_highgui -lopencv_core -lswscale -lavutil -lavcodec -lavformat

  It’s output on my system,

  cv::Mat [width=420, height=315, depth=0, channels=3, step=1260]
  
  I'll soon crash..
  
  Segmentation fault

  And that sample.jpg file’s details by identify tool,

  ~temporary/sample.jpg JPEG 420x315 420x315+0+0 8-bit sRGB 38.3KB 0.000u 0:00.000

  Please note that I’m trying to create a video out of a single image, just to keep things simple.

  #include <iostream>
  
  #include <cassert>
  
  using namespace std;
  
  
  
  extern "C" {
  
      #include <libavcodec></libavcodec>avcodec.h>
  
      #include <libswscale></libswscale>swscale.h>
  
      #include <libavformat></libavformat>avformat.h>
  
  }
  
  
  
  #include <opencv2></opencv2>core/core.hpp>
  
  #include <opencv2></opencv2>highgui/highgui.hpp>
  
  
  
  const string TEST_IMAGE = "/home/baris/temporary/sample.jpg";
  
  
  
  int main(int /*argc*/, char** argv)
  
  {
  
      av_register_all();
  
      avcodec_register_all();
  
  
  
      /**
  
       * Initialise the encoder
  
       */
  
      AVCodec *h264encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
  
      AVFormatContext *cv2avFormatContext = avformat_alloc_context();
  
  
  
      /**
  
       * Create a stream and allocate frames
  
       */
  
      AVStream *h264outputstream = avformat_new_stream(cv2avFormatContext, h264encoder);
  
      avcodec_get_context_defaults3(h264outputstream->codec, h264encoder);
  
      AVFrame *sourceAvFrame = av_frame_alloc(), *destAvFrame = av_frame_alloc();
  
      int got_frame;
  
  
  
      /**
  
       * Pixel formats for the input and the output
  
       */
  
      AVPixelFormat sourcePixelFormat = AV_PIX_FMT_BGR24;
  
      AVPixelFormat destPixelFormat = AV_PIX_FMT_YUV420P;
  
  
  
      /**
  
       * Create cv::Mat
  
       */
  
      cv::Mat cvFrame = cv::imread(TEST_IMAGE, CV_LOAD_IMAGE_COLOR);
  
      int width = cvFrame.size().width, height = cvFrame.size().height;
  
      cerr &lt;&lt; "cv::Mat [width=" &lt;&lt; width &lt;&lt; ", height=" &lt;&lt; height &lt;&lt; ", depth=" &lt;&lt; cvFrame.depth() &lt;&lt; ", channels=" &lt;&lt; cvFrame.channels() &lt;&lt; ", step=" &lt;&lt; cvFrame.step &lt;&lt; "]" &lt;&lt; endl;
  
  
  
      h264outputstream->codec->pix_fmt = destPixelFormat;
  
      h264outputstream->codec->width = cvFrame.cols;
  
      h264outputstream->codec->height = cvFrame.rows;
  
  
  
      /**
  
       * Prepare the conversion context
  
       */
  
      SwsContext *bgr2yuvcontext = sws_getContext(width, height,
  
                                                  sourcePixelFormat,
  
                                                  h264outputstream->codec->width, h264outputstream->codec->height,
  
                                                  h264outputstream->codec->pix_fmt,
  
                                                  SWS_BICUBIC, NULL, NULL, NULL);
  
  
  
      /**
  
       * Convert and encode frames
  
       */
  
      for (uint i=0; i &lt; 250; i++)
  
      {
  
          /**
  
           * Allocate source frame, i.e. input to sws_scale()
  
           */
  
          avpicture_alloc((AVPicture*)sourceAvFrame, sourcePixelFormat, width, height);
  
  
  
          for (int h = 0; h &lt; height; h++)
  
              memcpy(&amp;(sourceAvFrame->data[0][h*sourceAvFrame->linesize[0]]), &amp;(cvFrame.data[h*cvFrame.step]), width*3);
  
  
  
          /**
  
           * Allocate destination frame, i.e. output from sws_scale()
  
           */
  
          avpicture_alloc((AVPicture *)destAvFrame, destPixelFormat, width, height);
  
  
  
          sws_scale(bgr2yuvcontext, sourceAvFrame->data, sourceAvFrame->linesize,
  
                    0, height, destAvFrame->data, destAvFrame->linesize);
  
  
  
          /**
  
           * Prepare an AVPacket for encoded output
  
           */
  
          AVPacket avEncodedPacket;
  
          av_init_packet(&amp;avEncodedPacket);
  
          avEncodedPacket.data = NULL;
  
          avEncodedPacket.size = 0;
  
          // av_free_packet(&amp;avEncodedPacket); w/ or w/o result doesn't change
  
  
  
          cerr &lt;&lt; "I'll soon crash.." &lt;&lt; endl;
  
          if (avcodec_encode_video2(h264outputstream->codec, &amp;avEncodedPacket, destAvFrame, &amp;got_frame) &lt; 0)
  
              exit(1);
  
  
  
          cerr &lt;&lt; "Checking if we have a frame" &lt;&lt; endl;
  
          if (got_frame)
  
              av_write_frame(cv2avFormatContext, &amp;avEncodedPacket);
  
  
  
          av_free_packet(&amp;avEncodedPacket);
  
          av_frame_free(&amp;sourceAvFrame);
  
          av_frame_free(&amp;destAvFrame);
  
      }
  
  }
  
  </cassert></iostream>

  Thanks in advance !

  EDIT : And the stack trace after the crash,

  Thread 2 (Thread 0x7fffe5506700 (LWP 10005)):
  
  #0  0x00007ffff4bf6c5d in poll () at /lib64/libc.so.6
  
  #1  0x00007fffe9073268 in  () at /usr/lib64/libusb-1.0.so.0
  
  #2  0x00007ffff47010a4 in start_thread () at /lib64/libpthread.so.0
  
  #3  0x00007ffff4bff08d in clone () at /lib64/libc.so.6
  
  
  
  Thread 1 (Thread 0x7ffff7f869c0 (LWP 10001)):
  
  #0  0x00007ffff5ecc7dc in avcodec_encode_video2 () at /usr/lib64/libavcodec.so.56
  
  #1  0x00000000004019b6 in main(int, char**) (argv=0x7fffffffd3d8) at ../src/OpenCV2FFmpeg.cpp:99

  EDIT2 : Problem was that I hadn’t avcodec_open2() the codec as spotted by Ronald. Final version of the code is at https://github.com/barisdemiray/opencv2ffmpeg/, with leaks and probably other problems hoping that I’ll improve it while learning both libraries.

• WordPress Analytics plugin WP-Piwik reaches version 1.0.0 (and 50,000 active users)

  29 mai 2015, par André Bräkling — Plugins

  After six years of development, we are proud to announce the 1.0.0 release of our WP-Piwik WordPress plugin !

  Started as a simple plugin to show a selection of statistics within the WordPress dashboard, WP-Piwik has become a full Piwik integration plugin. The plugin automatically adds the Piwik tracking code to your WordPress sites. The plugin displays your analytics reports directly within the WordPress admin panel. WordPress networks (“multisite”), CDN URLs and the Piwik proxy script are also supported.

  According to WordPress.org the plugin is being used by more than 50,000 WordPress sites !

  

  This article explains how to install WP-Piwik and how to configure it to work with your Piwik instance.
  

  Install WP-Piwik

  You can get WP-Piwik using WordPress’ plugin management. Login to your WordPress admin dashboard and go to « Plugins » → « Add New ». Enter « WP-Piwik » into the search field at the top right, press enter and next to WP-Piwik choose « Install Now ».

  

  If you want to use WP-Piwik in your simple WordPress blog you can just click « Activate Plugin » and WP-Piwik will ask you to configure your Piwik connection.

  Running a WordPress network/multisite you can choose to « Network Activate » the plugin after the installation process. In this case, WP-Piwik will be a fully automated feature of your WordPress network automatically tracking your sites in the same Piwik instance in separate Websites.

  Alternatively you can download WP-Piwik manually from the WordPress website and upload all files to your `wp-content/plugins` directory.

  Configure your Piwik connection

  WP-Piwik lets you choose between three connection modes :

  • Self-hosted (HTTP API) : This is the default option for a self-hosted Piwik and should work for most configurations. You just have to know your Piwik URL, which is the URL you enter to access Piwik, and your auth token (see below). WP-Piwik will connect to Piwik using http(s)-requests.
  • Self-hosted (PHP API) : Choose this, if your self-hosted Piwik and WordPress are running on the same machine and you know the full server path to your Piwik instance. Beside the full server path, you also need to know your auth token (see below).
  • Cloud-hosted (Piwik Pro) : If you are using a cloud-hosted Piwik by Piwik Pro, you just need to know your user name and your auth token (see below).

  Setting up WP-Piwik

  To configure WP-Piwik you will need to specify your Authentication token.

  • If the site you want to track in Piwik is already configured in your Piwik, you only need to specify a token_auth for a user with `view` permission.
  • If you want WP-Piwik to create the website in Piwik (or if you use WP-Piwik in network mode which requires to be able to configure your sites), you should specify a token_auth which has Super User access (after the setting up phase is completed you can set the authentication token back to the token of a `view` user).

  To find your token_auth in Piwik, click on your user name in the right right corner of your Piwik dashboard, then click the « API » in the left menu. The API page displays your auth token in a colored box, just behind the “&token_auth=” string. The screenshot below shows the token_auth anonymous, but your real one will be an alpha numerous random string like a1ec31524a8eabc7a546d71d68b28d17.

  

  That’s it. After you entered your connection data and submitted the form, WP-Piwik will welcome you with some information :

  

  You can now start to configure WP-Piwik and enable the tracking code. Learn about any setting by clicking on the small question mark sign. If you have any problem configuring or using WP-Piwik feel free to use the WordPress support forum related to WP-Piwik.

  Translating WP-Piwik

  We invite you to join our translation community at Transifex and help to translate WP-Piwik in more languages !

  Happy WordPress Analytics !

• WordPress Analytics plugin WP-Piwik reaches version 1.0.0 (and 50,000 active users)

  29 mai 2015, par André Bräkling — Plugins

  After six years of development, we are proud to announce the 1.0.0 release of our WP-Piwik WordPress plugin !

  Started as a simple plugin to show a selection of statistics within the WordPress dashboard, WP-Piwik has become a full Piwik integration plugin. The plugin automatically adds the Piwik tracking code to your WordPress sites. The plugin displays your analytics reports directly within the WordPress admin panel. WordPress networks (“multisite”), CDN URLs and the Piwik proxy script are also supported.

  According to WordPress.org the plugin is being used by more than 50,000 WordPress sites !

  

  This article explains how to install WP-Piwik and how to configure it to work with your Piwik instance.
  

  Install WP-Piwik

  You can get WP-Piwik using WordPress’ plugin management. Login to your WordPress admin dashboard and go to « Plugins » → « Add New ». Enter « WP-Piwik » into the search field at the top right, press enter and next to WP-Piwik choose « Install Now ».

  

  If you want to use WP-Piwik in your simple WordPress blog you can just click « Activate Plugin » and WP-Piwik will ask you to configure your Piwik connection.

  Running a WordPress network/multisite you can choose to « Network Activate » the plugin after the installation process. In this case, WP-Piwik will be a fully automated feature of your WordPress network automatically tracking your sites in the same Piwik instance in separate Websites.

  Alternatively you can download WP-Piwik manually from the WordPress website and upload all files to your `wp-content/plugins` directory.

  Configure your Piwik connection

  WP-Piwik lets you choose between three connection modes :

  • Self-hosted (HTTP API) : This is the default option for a self-hosted Piwik and should work for most configurations. You just have to know your Piwik URL, which is the URL you enter to access Piwik, and your auth token (see below). WP-Piwik will connect to Piwik using http(s)-requests.
  • Self-hosted (PHP API) : Choose this, if your self-hosted Piwik and WordPress are running on the same machine and you know the full server path to your Piwik instance. Beside the full server path, you also need to know your auth token (see below).
  • Cloud-hosted (Piwik Pro) : If you are using a cloud-hosted Piwik by Piwik Pro, you just need to know your user name and your auth token (see below).

  Setting up WP-Piwik

  To configure WP-Piwik you will need to specify your Authentication token.

  • If the site you want to track in Piwik is already configured in your Piwik, you only need to specify a token_auth for a user with `view` permission.
  • If you want WP-Piwik to create the website in Piwik (or if you use WP-Piwik in network mode which requires to be able to configure your sites), you should specify a token_auth which has Super User access (after the setting up phase is completed you can set the authentication token back to the token of a `view` user).

  To find your token_auth in Piwik, click on your user name in the right right corner of your Piwik dashboard, then click the « API » in the left menu. The API page displays your auth token in a colored box, just behind the “&token_auth=” string. The screenshot below shows the token_auth anonymous, but your real one will be an alpha numerous random string like a1ec31524a8eabc7a546d71d68b28d17.

  

  That’s it. After you entered your connection data and submitted the form, WP-Piwik will welcome you with some information :

  

  You can now start to configure WP-Piwik and enable the tracking code. Learn about any setting by clicking on the small question mark sign. If you have any problem configuring or using WP-Piwik feel free to use the WordPress support forum related to WP-Piwik.

  Translating WP-Piwik

  We invite you to join our translation community at Transifex and help to translate WP-Piwik in more languages !

  Happy WordPress Analytics !