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• FFMPEG : AV out of sync when writing a part of a video to a new file

  30 mars 2017, par IT_Layman

  I’m developing a data preprocessing program for a computer vision project using FFMPEG and Face detection API. In this program, I need to extract the shots that contain human faces from a given input video file and output them into a new file. But when I played the output video file generated by that program, the video and audio track was out of sync. I think a possible reason is that the timestamp of video frame or audio frame is set incorrectly, but I can’t fix it by myself as I’m not very familiar with FFMPEG library, Please help me solving this out-of-sync issue.

  To simplify the code shown below, I have removed all face detection code and use an empty function called faceDetect to represent it instead.

  // ffmpegAPI.cpp : Defines the entry point for the console application.
  
  //
  
      #include "stdafx.h"
  
      #include <iostream>
  
  
  
      extern "C" {
  
      #include <libavutil></libavutil>opt.h>
  
      #include <libavcodec></libavcodec>avcodec.h>
  
      #include <libavformat></libavformat>avformat.h>
  
      #include <libavutil></libavutil>avutil.h>
  
      #include <libavutil></libavutil>channel_layout.h>
  
      #include <libavutil></libavutil>common.h>
  
      #include <libavutil></libavutil>imgutils.h>
  
      #include <libavutil></libavutil>mathematics.h>
  
      #include <libavutil></libavutil>samplefmt.h>
  
      #include <libavutil></libavutil>pixdesc.h>
  
      #include <libswscale></libswscale>swscale.h>
  
  
  
  }
  
  bool faceDetect(AVFrame *frame)
  
  {
  
      /*...*/
  
      return true;
  
  }
  
  int main(int argc, char **argv)
  
  {
  
      int64_t videoPts = 0, audioPts = 0;
  
      int samples_count = 0;
  
      AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx = NULL;
  
      AVOutputFormat *ofmt = NULL;
  
      AVPacket pkt;
  
      AVFrame *frame = NULL;
  
      int videoindex = -1; int audioindex = -1;
  
      double videoTime = DBL_MAX;
  
      const char *in_filename, *out_filename;
  
      int ret, i;
  
      in_filename = "C:\\input.flv";//Input file name
  
      out_filename = "C:\\output.avi";//Output file name
  
      av_register_all();
  
      //Open input file
  
      if ((ret = avformat_open_input(&amp;ifmt_ctx, in_filename, 0, 0)) &lt; 0) {
  
          fprintf(stderr, "Could not open input file '%s'", in_filename);
  
          goto end;
  
      }
  
      //Find input streams
  
      if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) &lt; 0) {
  
          fprintf(stderr, "Failed to retrieve input stream information");
  
          goto end;
  
      }
  
      //Retrive AV stream information
  
      for (i = 0; i &lt; ifmt_ctx->nb_streams; i++)
  
      {
  
          AVStream *stream;
  
          AVCodecContext *codec_ctx;
  
          stream = ifmt_ctx->streams[i];//Get current stream
  
          codec_ctx = stream->codec;//Get current stream codec
  
          if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO)
  
          {
  
              videoindex = i;//video stream index
  
          }
  
          else if (codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO)
  
          {
  
              audioindex = i;//audio stream index
  
          }
  
          if (videoindex == -1)//no video stream is found
  
          {
  
              printf("can't find video stream\n");
  
              goto end;
  
  
  
          }
  
      }
  
      av_dump_format(ifmt_ctx, 0, in_filename, 0);
  
      //Configure output
  
      avformat_alloc_output_context2(&amp;ofmt_ctx, NULL, NULL, out_filename);
  
      if (!ofmt_ctx) {
  
          fprintf(stderr, "Could not create output context\n");
  
          ret = AVERROR_UNKNOWN;
  
          goto end;
  
      }
  
      ofmt = ofmt_ctx->oformat;
  
      //Configure output streams
  
      for (i = 0; i &lt; ifmt_ctx->nb_streams; i++) {//Traversal input streams
  
          AVStream *in_stream = ifmt_ctx->streams[i];//Get current stream
  
          AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);//Create a corresponding output stream
  
          if (!out_stream) {
  
              fprintf(stderr, "Failed allocating output stream\n");
  
              ret = AVERROR_UNKNOWN;
  
              goto end;
  
          }
  
          //Copy codec from current input stream to corresponding output stream
  
          ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
  
          if (ret &lt; 0) {
  
              fprintf(stderr, "Failed to copy context from input to output stream codec context\n");
  
              goto end;
  
          }
  
          if (i == videoindex)//Video stream
  
          {
  
              if (out_stream->codec->codec_id == AV_CODEC_ID_H264)
  
              {
  
                  out_stream->codec->me_range = 16;
  
                  out_stream->codec->max_qdiff = 4;
  
                  out_stream->codec->qmin = 10;
  
                  out_stream->codec->qmax = 51;
  
                  out_stream->codec->qcompress = 1;
  
  
  
              }
  
          }
  
          AVCodecContext *codec_ctx = out_stream->codec;
  
          if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO
  
              || codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
  
              //Find codec encoder
  
              AVCodec *encoder = avcodec_find_encoder(codec_ctx->codec_id);
  
              if (!encoder) {
  
                  av_log(NULL, AV_LOG_FATAL, "Necessary encoder not found\n");
  
                  ret = AVERROR_INVALIDDATA;
  
                  goto end;
  
              }
  
              //Open encoder
  
              ret = avcodec_open2(codec_ctx, encoder, NULL);
  
              if (ret &lt; 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", i);
  
                  goto end;
  
              }
  
              out_stream->codec->codec_tag = 0;
  
              if (ofmt_ctx->oformat->flags &amp; AVFMT_GLOBALHEADER)
  
                  out_stream->codec->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
  
          }
  
          //Open the decoder for input stream
  
          codec_ctx = in_stream->codec;
  
          if (codec_ctx->codec_type == AVMEDIA_TYPE_VIDEO
  
              || codec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
  
              ret = avcodec_open2(codec_ctx,
  
                  avcodec_find_decoder(codec_ctx->codec_id), NULL);
  
              if (ret &lt; 0) {
  
                  av_log(NULL, AV_LOG_ERROR, "Failed to open decoder for stream #%u\n", i);
  
              }
  
          }
  
      }
  
      av_dump_format(ofmt_ctx, 0, out_filename, 1);
  
      //Open output file for writing
  
      if (!(ofmt->flags &amp; AVFMT_NOFILE)) {
  
          ret = avio_open(&amp;ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
  
          if (ret &lt; 0) {
  
              fprintf(stderr, "Could not open output file '%s'", out_filename);
  
              goto end;
  
          }
  
      }
  
  
  
      //Write video header
  
      ret = avformat_write_header(ofmt_ctx, NULL);
  
      if (ret &lt; 0) {
  
          fprintf(stderr, "Error occurred when opening output file\n");
  
          goto end;
  
      }
  
      //Write frames in a loop
  
      while (1) {
  
          AVStream *in_stream, *out_stream;
  
          //Read one frame from the input file
  
          ret = av_read_frame(ifmt_ctx, &amp;pkt);
  
          if (ret &lt; 0)
  
              break;
  
          in_stream = ifmt_ctx->streams[pkt.stream_index];//Get current input stream
  
          out_stream = ofmt_ctx->streams[pkt.stream_index];//Get current output stream
  
          if (pkt.stream_index == videoindex)//video frame
  
          {
  
              int got_frame;
  
              frame = av_frame_alloc();
  
              if (!frame) {
  
                  ret = AVERROR(ENOMEM);
  
                  break;
  
              }
  
              //Readjust packet timestamp for decoding
  
              av_packet_rescale_ts(&amp;pkt,
  
                  in_stream->time_base,
  
                  in_stream->codec->time_base);
  
              //Decode video frame
  
              int len = avcodec_decode_video2(in_stream->codec, frame, &amp;got_frame, &amp;pkt);
  
              if (len &lt; 0)
  
              {
  
                  av_frame_free(&amp;frame);
  
                  av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
  
                  break;
  
              }
  
              if (got_frame)//Got a decoded video frame
  
              {
  
                  int64_t pts = av_frame_get_best_effort_timestamp(frame);
  
                  //determine if the frame image contains human face
  
                  bool result = faceDetect(frame);
  
                  if (result) //face contained
  
                  {
  
                      videoTime = pts* av_q2d(out_stream->time_base);
  
                      frame->pts = videoPts++;//Set pts of video frame
  
                      AVPacket enc_pkt;
  
                      av_log(NULL, AV_LOG_INFO, "Encoding video frame\n");
  
                      //Create packet for encoding
  
                      enc_pkt.data = NULL;
  
                      enc_pkt.size = 0;
  
                      av_init_packet(&amp;enc_pkt);
  
                      //Encoding frame
  
                      ret = avcodec_encode_video2(out_stream->codec, &amp;enc_pkt,
  
                          frame, &amp;got_frame);
  
                      av_frame_free(&amp;frame);
  
                      if (!(got_frame))
  
                          ret = 0;
  
                      /* Configure encoding properties */
  
                      enc_pkt.stream_index = videoindex;
  
                      av_packet_rescale_ts(&amp;enc_pkt,
  
                          out_stream->codec->time_base,
  
                          out_stream->time_base);
  
                      av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");
  
                      /* Write encoded frame */
  
                      ret = av_interleaved_write_frame(ofmt_ctx, &amp;enc_pkt);
  
                      if (ret &lt; 0)
  
                          break;
  
                  }
  
                  else //no face contained
  
                  {
  
                      //Set the videoTime as maximum double value, 
  
                      //making the corresponding audio frame not been processed
  
                      if (videoTime &lt; DBL_MAX)
  
                          videoTime = DBL_MAX;
  
                  }
  
  
  
              }
  
              else
  
              {
  
                  av_frame_free(&amp;frame);
  
              }
  
          }
  
          else//Audio frame
  
          {
  
              //Get current frame time
  
              double audioTime = pkt.pts * av_q2d(in_stream->time_base);
  
              if (audioTime >= videoTime)
  
              {//The current frame should be written into output file
  
                  int got_frame;
  
                  frame = av_frame_alloc();
  
                  if (!frame) {
  
                      ret = AVERROR(ENOMEM);
  
                      break;
  
                  }
  
                  //Readjust packet timestamp for decoding
  
                  av_packet_rescale_ts(&amp;pkt,
  
                      in_stream->time_base,
  
                      in_stream->codec->time_base);
  
                  //Decode audio frame
  
                  int len = avcodec_decode_audio4(in_stream->codec, frame, &amp;got_frame, &amp;pkt);
  
                  if (len &lt; 0)
  
                  {
  
                      av_frame_free(&amp;frame);
  
                      av_log(NULL, AV_LOG_ERROR, "Decoding failed\n");
  
                      break;
  
                  }
  
                  if (got_frame)//Got a decoded audio frame
  
                  {
  
                      //Set pts of audio frame
  
                      frame->pts = audioPts;
  
                      audioPts += frame->nb_samples;
  
                      AVPacket enc_pkt;
  
                      av_log(NULL, AV_LOG_INFO, "Encoding audio frame");
  
                      //Create packet for encoding
  
                      enc_pkt.data = NULL;
  
                      enc_pkt.size = 0;
  
                      av_init_packet(&amp;enc_pkt);
  
                      //Encode audio frame
  
                      ret = avcodec_encode_audio2(out_stream->codec, &amp;enc_pkt,
  
                          frame, &amp;got_frame);
  
                      av_frame_free(&amp;frame);
  
                      if (!(got_frame))
  
                          ret = 0;
  
                      /* Configure encoding properties */
  
                      enc_pkt.stream_index = audioindex;
  
                      av_packet_rescale_ts(&amp;enc_pkt,
  
                          out_stream->codec->time_base,
  
                          out_stream->time_base);
  
                      av_log(NULL, AV_LOG_DEBUG, "Muxing frame\n");
  
                      /* Write encoded frame */
  
                      ret = av_interleaved_write_frame(ofmt_ctx, &amp;enc_pkt);
  
                      if (ret &lt; 0)
  
                          break;
  
                  }
  
                  else //Shouldn't be written
  
                  {
  
                      av_frame_free(&amp;frame);
  
                  }
  
              }
  
          }
  
          av_packet_unref(&amp;pkt);
  
      }
  
      //Write video trailer
  
      av_write_trailer(ofmt_ctx);
  
  end://Clean up
  
      av_log(NULL, AV_LOG_INFO, "Clean up\n");
  
      av_frame_free(&amp;frame);
  
      for (i = 0; i &lt; ifmt_ctx->nb_streams; i++) {
  
          avcodec_close(ifmt_ctx->streams[i]->codec);
  
          if (ofmt_ctx &amp;&amp; ofmt_ctx->nb_streams > i &amp;&amp; ofmt_ctx->streams[i] &amp;&amp; ofmt_ctx->streams[i]->codec)
  
              avcodec_close(ofmt_ctx->streams[i]->codec);
  
      }
  
      avformat_close_input(&amp;ifmt_ctx);
  
      /* Close output file */
  
      if (ofmt_ctx &amp;&amp; !(ofmt_ctx->oformat->flags &amp; AVFMT_NOFILE))
  
          avio_closep(&amp;ofmt_ctx->pb);
  
      avformat_free_context(ofmt_ctx);
  
      if (ret &lt; 0 &amp;&amp; ret != AVERROR_EOF) {
  
          char buf[256];
  
          av_strerror(ret, buf, sizeof(buf));
  
          av_log(NULL, AV_LOG_ERROR, "Error occurred:%s\n", buf);
  
          system("Pause");
  
          return 1;
  
      }
  
      //Program end
  
      printf("The End.\n");
  
      system("Pause");
  
      return 0;
  
  }
  
  </iostream>

• Need Help. audio API choice

  6 mars 2017, par Wyatt

  What API can I use to determine a single digit representing an entire mp3’s average amplitude of a range of frequencies ? Ex) 100 Hz - 200 Hz should output a single digit, 5dB.

• How Funnel for Piwik Analytics enriches your Piwik experience giving you ultimate insights and debugging capabilities

  13 janvier 2017, par InnoCraft — Community

  No matter what type of website or app you have, whether you are trying to get your users to sign up for something or sell products, there is a certain number of steps your visitors have to go through. On every step you lose visitors and therefore potential revenue and conversions. Therefore it is critical to know where your visitors actually follow those steps in your website or app, where you lose them and where your visitors maybe get confused. By defining a funnel, you can improve your conversion rates, sales and revenue as you can exactly determine where you lose your visitors in converting your goal or a sale.

  A Funnel defines a series of steps that you expect your visitors to take on their way to converting a goal. Funnels, a premium feature for Piwik developed by InnoCraft, lets you create funnels to get the data you need to improve your websites and mobile apps. Learn more about Funnel.

  In this blog post we will cover the reports the Funnel plugin provides. The next blog post shows you how to configure and validate your funnel in Piwik.

  

  Integration in Goal reports

  At Piwik and InnoCraft, we usually start looking into our goal reports. Funnel integrates directly into each goal reporting page giving you a quick overview how your funnel is doing. This saves us a lot of time as we don’t have to separately look into each funnel page and only takes us maybe an additional second to keep an eye on our funnels. By clicking on the headline or “View funnel report” link, you can directly go to the funnel report to get a more detailed report if you notice any spike in the evolution of the conversions or conversion rate.

  

  Getting an overall Funnel overview

  Next we usually go to the “Funnel Overview” page where it shows a list of all activated Funnels and their performance over time. You will find the look familiar as it is similar to the “Goals Overview” page. If we find something unusual there, for example any spikes, we usually directly click on the headline of the Funnel to go to the detailed Funnel report. You can also choose a funnel from the left reporting menu or search for a funnel by entering the shortcut “f”.

  

  Viewing a funnel report

  A funnel reporting page looks very similar to a Goal reporting page. It starts with an evolution graph and sparklines showing you the performance of your funnel over time.

  

  In the evolution graph you can select the metrics you want to plot. We usually have an eye on the funnel conversion rate and the number of “Funnel entries” or the number of “Funnel conversions”. The conversion rate alone does not show you how your funnel is performing. Imagine the rate is always stable at around 20% and you might think everything is alright, but if the number of visitors that take part in your funnel goes down, you might have a problem as the number of funnel conversions actually decreases even though the rate is the same. So we recommend to not only have a look at the conversion rate. The report will remember the metrics you want to plot each time you open it so you don’t have to re-select them over and over again.

  

  The funnel overview

  In the funnel overview we are giving you more details about the funnel and goal related conversion metrics so you don’t have to switch between the goal and funnel report and compare them easily.

  When you analyze a funnel report, you might not always remember how the funnel is configured. Even though you specify names for each step you sometimes need to know on which pages a certain step will be activated. By clicking on the funnel summary link you can quickly look into the funnel configuration and also see all important metrics at a glance in a simple table without having to scroll.

  

  You might also notice the Visitor Log link which will show you all actions for all visitors that have entered this funnel. This lets you really understand how your visitors navigate through your website and how they proceeded, exited or converted your funnel on a visitor level.

  

  The Funnel visualization

  Below the funnel overview you can visually see where your visitors entered, proceeded, converted and exited your funnel. We kept the UI clean so you can focus on the important things.

  Most tools only give you the pages where visitors have entered your funnel but we do better and also show you the list of external referrers used by visitors to enter your funnel directly (marketing campaigns, search engines or other websites). Also we do not only show only the top 5 pages but up to 100 pages and 50 referrers (more can be configured if needed). When you hover a row, you will not only see the number of hits but also the percentage each row has contributed to the entries. Here you want to look and understand how your visitors enter your funnel and based on the data maybe invest in successful referrers, campaigns and pages. If the pages or referrers you expect to see there don’t show up, your users might not understand the path you had in mind for them.

  

  Next you may notice how many visits have gone through each step, in this case 3487 visits. The green and red bar lets you quickly identify how many of your visitors have proceeded to the next step (green) compared to how many have exited the funnel at this step (red). Ideally, most of the bar is green and not red indicating that more visitors proceed to the next step than they exit.

  

  Now the next feature is really valuable. When you hover the step title or the number of visits, you will notice that two icons appear :

  

  Those two little icons are really powerful and give you even more insights to really dig into all the data. The left icon shows you the visitor log showing all actions of each visitor that have participated in this particular funnel step. This means for each step you get to see all the details and actions of each visitor. This lets you really debug and understand problems in your funnel.

  At InnoCraft, we understand that plain numbers are often not so valuable. Only the evolution over time, when you put the numbers in relation to something else you can really understand how your website is doing. The icon to the right lets you do exactly this, it lets you view the row evolution for each funnel step. We are sure you will enjoy this feature. It lets you explore how each funnel step is doing over time. For example the number of entries for a step or how many proceeded to the next step from here over time. Here you ideally want to see that the “Proceeded Rate” increases over time, meaning more and more visitors actually proceed to the next step instead of exiting it.

  

  We are sure you will really love those features that give you just those extra insights that other tools don’t give you.

  On the right you can find out where your visitors went to, if they did not proceed any further in the funnel. This lets you better understand why they left the funnel and did not proceed any further.

  

  At the end of the funnel report you find again the number of conversions and the conversion rate. Here we recommend looking into the visitor log when you hover the name of the last step as you can analyze how each visitor converted this funnel in detail.

  

  Applying segments

  Funnels lets you apply any Piwik segment to the Funnel report allowing you to dice your visitors multiplying the value you get out of Funnel. For example you may want to apply a segment and analyze the funnel for visitors that have visited your website or mobile app for the first time vs. recurring visitors. Sometimes it may be interesting how visitors from different countries go through your funnel, the possibilities are endless. We really recommend to take advantage of segments to understand your different target groups even better.

  The plugin also adds some new segments to your Piwik letting you segment any Piwik report by visitors that have participated in a funnel or participated in a particular funnel step. For example you could go to the “Visitors => Locations” report and apply a segment for your funnel to see which countries have participated or converted most in your funnel.

  Widgets, Scheduled Reports, and more.

  This is not where the fun ends. Funnels defines new widgets that you can add to your dashboard or export it into a third party website. You can set up scheduled reports to receive the Funnel report automatically via email or sms or download the report to share it with your colleagues. It works also very well with Custom Alerts and you can view the Funnel report in the Piwik Mobile app. You can manage Funnels via HTTP API and also fetch all Funnel reports via the HTTP Reporting API. The plugin is really nicely integrated into Piwik we will need some more blog posts to show you all the ways Funnels advances your Piwik experience and how it lets you dig into all the data so you can increase your conversions and sales based on this data.

  How to get Funnels and related features

  You can get Funnels on the Piwik Marketplace. If you want to learn more about Funnels you might be also interested in the Funnel User Guide and the Funnel FAQ.

  Similar to Funnels we also offer Users Flow which lets you visualize the flow of your users and visitors across several interactions.