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• avformat/rtpdec_jpeg : fix low contrast image on low quality setting

  24 mars 2016, par Ico Doornekamp

  avformat/rtpdec_jpeg : fix low contrast image on low quality setting
  Original mail and my own followup on ffmpeg-user earlier today :
  I have a device sending out a MJPEG/RTP stream on a low quality setting.
  
  Decoding and displaying the video with libavformat results in a washed
  
  out, low contrast, greyish image. Playing the same stream with VLC results
  
  in proper color representation.
  Screenshots for comparison :
    http://zevv.nl/div/libav/shot-ffplay.jpg
  
    http://zevv.nl/div/libav/shot-vlc.jpg
  A pcap capture of a few seconds of video and SDP file for playing the
  
  stream are available at
    http://zevv.nl/div/libav/mjpeg.pcap
  
    http://zevv.nl/div/libav/mjpeg.sdp
  I believe the problem might be in the calculation of the quantization
  
  tables in the function create_default_qtables(), the attached patch
  
  solves the issue for me.
  The problem is that the argument ’q’ is of the type uint8_t. According to the
  
  JPEG standard, if 1 <= q <= 50, the scale factor ’S’ should be 5000 / Q.
  
  Because the create_default_qtables() reuses the variable ’q’ to store the
  
  result of this calculation, for small values of q < 19, q wil subsequently
  
  overflow and give wrong results in the calculated quantization tables. The
  
  patch below uses a new variable ’S’ (same name as in RFC2435) with the proper
  
  range to store the result of the division.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/rtpdec_jpeg.c

• rtpdec_jpeg : fix low contrast image on low quality setting

  24 mars 2016, par Ico Doornekamp

  rtpdec_jpeg : fix low contrast image on low quality setting
  The problem is that the argument ’q’ is of the type uint8_t.
  
  According to the JPEG standard, if 1 <= q <= 50, the scale factor
  
  ’S’ should be 5000 / Q. Because the create_default_qtables() reuses
  
  the variable ’q’ to store the result of this calculation, for small
  
  values of q < 19, q wil subsequently overflow and give wrong results
  
  in the calculated quantization tables.
  Instead, use a new variable ’S’ (same name as in RFC2435) with the
  
  proper range to store the result of the division.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavformat/rtpdec_jpeg.c

• ffmpeg channels don't work (PHP)

  15 avril 2016, par Y.Saad

  I have a lot of channels with " ffmpeg " (4 channels) that start automatically, I create a code for show the first channel and after 5 seconds show the second .. Etc All things as right but I have a small problem the seconds channel doesn’t start automatically, I need to make stop to the first channel

  Code for 4 channel work 100% but without function for show first channel and after 5 seconds show the second ... Etc

  <?php
  
  
  
  ffmpeg -i http://clay24.webhop.net:8000/live/mario/mario/13.ts -i http://clay24.webhop.net:8000/live/mario/mario/12.ts -i http://clay24.webhop.net:8000/live/mario/mario/10.ts -map 0 -c:a aac -b:a 64k -strict -2 -preset fast -crf 25 -vcodec libx264 -f flv rtmp://178.33.231.108:1989/mylive/1 -map 1 -c:a aac -b:a 64k -strict -2 -preset fast -crf 25 -vcodec libx264 -f flv rtmp://178.33.231.108:1989/mylive/21 -map 2 -c:a aac -b:a 64k -strict -2 -preset fast -crf 25 -vcodec libx264 -f flv rtmp://178.33.231.108:1989/mylive/24
  
  
  
  ?>

  the second code with functions

  <?php
  
  echo'
  
      <code class="echappe-js">&lt;script&gt;<br />
  
  <br />
  
                  window.addEventListener(&quot;load&quot;, function() {<br />
  
  <br />
  
  var urls = iframes = [ &quot;'; ffmpeg -i http://mygameravatar.zapto.org:43666/live/test1/test2/81.ts -c:a aac -b:a 64k -preset fast -crf 25 -vcodec libx264 -f flv rtmp://178.33.231.108:1989/mylive/2 <br />
  
          echo '];<br />
  
  <br />
  
  var iframes = document.querySelectorAll(&quot;div&quot;);<br />
  
  <br />
  
  var n = 0;<br />
  
  <br />
  
  var interval = setInterval(function() {<br />
  
    <br />
  
    iframes[++n].src = urls[n - 1];<br />
  
    iframes[n].style.display = &quot;block&quot;;<br />
  
    console.log(n);<br />
  
    if (n === iframes.length -1) {<br />
  
      clearInterval(interval);<br />
  
      console.log(&quot;all iframes loaded&quot;)<br />
  
    }<br />
  
    <br />
  
  }, 5000)<br />
  
  <br />
  
  })<br />
  
          &lt;/script&gt;
  
  	’ ;
  	ffmpeg -i http://mygameravatar.zapto.org:43666/live/test1/test2/297.ts -c:a aac -b:a 64k -preset fast -crf 25 -vcodec libx264 -f flv rtmp ://178.33.231.108:1989/mylive/1
  	echo ’
  
  ’ ;
  
   ?>