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• OpenCV libopencv_core.so.2.4.1 File Not Found

  14 novembre 2013, par benrules2

  I am trying to setup OpenCV v2.4.1 with FFMPEG v0.11 support on Scientific Linux SL release 5.0 (Boron), and I am running into a problem with a missing file that seems completely undocumented. The error I am getting is as follows :

  -- Install configuration: "Release"
  
  
  
  -- Up-to-date: /home/s18/s1138832/OpenCV/include/opencv/cv.h
  
  -- Up-to-date: /home/s18/s1138832/OpenCV/include/opencv/cxmisc.h
  
  -- Up-to-date: /home/s18/s1138832/OpenCV/include/opencv/cvwimage.h
  
  -- Up-to-date: /home/s18/s1138832/OpenCV/include/opencv2/opencv.hpp
  
  CMake Error at modules/core/cmake_install.cmake:63 (FILE):
  
  file INSTALL cannot find file
  
    "/home/s18/s1138832/OpenCV/lib/libopencv_core.so.2.4.1" to install.
  
  Call Stack (most recent call first):
  
    modules/cmake_install.cmake:57 (INCLUDE)
  
    cmake_install.cmake:56 (INCLUDE)

  I honestly don't know where to begin troubleshooting this at this point. I successfully installed without ffmpeg a few days ago, but now I can't even install with ffmpeg support set to off.

  The files that link to the missing library are :

  lrwxrwxrwx 1 s1138832 s18      21 Jun 17 18:26 libopencv_core.so ->    libopencv_core.so.2.4
  
  lrwxrwxrwx 1 s1138832 s18      23 Jun 17 18:26 libopencv_core.so.2.4 -> libopencv_core.so.2.4.1

  Any advice or prods in the right direction would be much appreciated. I would also be happy to provide more info on whatever interesting details I may have omitted.

  UPDATES : This website seems to have the same error, but I can't read it and translations patchy - http://www.opencv.org.cn/forum/viewtopic.php?f=1&t=15664 ( http://translate.google.com/translate?sl=auto&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.opencv.org.cn%2Fforum%2Fviewtopic.php%3Ff%3D1%26t%3D15664&act=url )

  libopencv_core.so.2.4.1 exists after "make", but "make install" deletes it somehow. I copied it and added it again, but it didn't change anything

• How to use AVCodecContext::skip_frame ?

  28 mai 2012, par Denis Loh

  I am developing a Video over IP telephone client which is using ffmpeg libavcodec to decode h.264 video streams. I am facing the issue that audio and video are getting asynch during high network load (due a parallel upload or something similar) or short network interruptions.

  I get the following message by ffmpeg : Increasing reorder buffer to 16.

  This message comes very seldom and when it comes, I get a high delay of approx. 1 second after the appropriate audio. I googled hours and days and only found that the decoding performance is much too low to decode the frames in time. However, the CPU load is not that high and the issue occurs at any frame rate and any frame resolution. Always with the same effect.

  The only thing I believe could solve the problem is to tell the decoder to speed up by dropping some framess.

  Can this be done by using AVCodecContext::skip_frame ? If so, how does it work ? How do I avoid the message above or better how do I react on that ?

  Thank you for your help !

• Transcoding & displaying user-uploaded videos for cross-browser/platform compatibility

  5 avril 2012, par Jonathan Amend

  I want to display user-uploaded videos in high quality on different browsers/platforms. I think I have a pretty good start, but there are a few issues. I have at my disposal ffmpeg 0.10 (called from PHP) and jwPlayer 5.8 (licensed).

  Ideally I would like to support :

  • Browsers with Flash 9+
  • Modern Firefox/Chrome/Safari without Flash
  • iOS 4.1+
  • Android 2.2+

  My current transcoding commands are :

  $commands = array(
  
      'flv' => "/usr/bin/ffmpeg -y -i {$sourceFile} -b 500k -ar 22050 -ab 64 {$tmpFileName}.flv 2>&1",
  
      'webm' => "/usr/bin/ffmpeg -i {$sourceFile} -acodec libvorbis -ac 2 -ab 96k -ar 44100 -b 500k {$tmpFileName}.webm 2>&1",
  
      'mp4' => "/usr/bin/ffmpeg -i {$sourceFile} -acodec libfaac -ab 96k -vcodec libx264 -level 21 -refs 2 -vf 'scale=trunc(ih*a/2)*2:trunc(iw/a/2)*2' -b 500k -bt 1000k -threads 0 -f mp4 {$tmpFileName}.pre.mp4 2>&1",
  
      'jpg' => "/usr/bin/ffmpeg -y -i {$sourceFile} -ss 5 -vcodec mjpeg -vframes 1 -an -f rawvideo {$tmpFileName}.jpg 2>&1"
  
  );
  
  
  
  $fastStartCommand = "/usr/bin/qt-faststart {$tmpFileName}.pre.mp4 {$tmpFileName}.mp4");

  My current display code is this :

  <video controls="controls" width="{$width}" height="{$height}" poster="{$fileJPG}" style="width: {$width}px; height: {$height}px;">
  
      <source src="{$fileMP4}" type="video/mp4" data-ext="mp4"></source>
  
      <source src="{$fileWEBM}" type="video/webm" data-ext="webm"></source>
  
      <a href="http://stackoverflow.com/feeds/tag/{$fileMP4}" title="Play Video">
  
          <img border="0" src="http://stackoverflow.com/feeds/tag/{$fileJPG}" width='0' height='0' alt="Play Video" />
  
      </a>
  
  </video>
  
  <code class="echappe-js">&lt;script type=&quot;text/javascript&quot;&gt;<br />
  
  swfobject.embedSWF(<br />
  
      &amp;#39;/flash/jwPlayer.swf&amp;#39;,<br />
  
      &amp;#39;video&amp;#39;,<br />
  
      {$width},<br />
  
      {$height},<br />
  
      &amp;#39;9.0.0&amp;#39;,<br />
  
      &amp;#39;&amp;#39;,<br />
  
      {<br />
  
          file: &amp;#39;{$fileFLV}&amp;#39;,<br />
  
          width: {$width},<br />
  
          height: {$height},<br />
  
          provider: &amp;#39;video&amp;#39;,<br />
  
          stretching: &amp;#39;uniform&amp;#39;,<br />
  
          smoothing: &amp;#39;true&amp;#39;,<br />
  
          dock: &amp;#39;true&amp;#39;<br />
  
      },<br />
  
      {<br />
  
          menu: &amp;#39;false&amp;#39;,<br />
  
          allowfullscreen: &amp;#39;true&amp;#39;,<br />
  
          allowscriptaccess: &amp;#39;always&amp;#39;,<br />
  
          allownetworking: &amp;#39;always&amp;#39;,<br />
  
          wmode: &amp;#39;transparent&amp;#39;<br />
  
      }<br />
  
  );<br />
  
  &lt;/script&gt;
  
  

  The idea is to prefer the Flash player (we have many custom skins that we would like to keep using), then fall back to HTML 5 video, and if that fails, show the JPEG with a link to the mp4 file (that seems to work as a last-ditch effort for iOS 2/3 and old browsers so they can at least play the video by launching QuickTime).

  The main issues that I'm not sure how to solve right now are :

  • How can I show a higher quality video in Flash ? I tried using the mp4 video instead of the flv but it doesn't work and I only get sound, no video. I think Flash is supposed to support h.264 these days, but how ? And do I have to use a different transcoding method for older and newer versions of Flash ?
  • How can I transcode the video with better quality ? Right now I am using the same bitrate for all resolutions. Any chance there is a way for ffmpeg to adjust the bitrate automatically ? Or can I detect and match the resolution of the uploaded video to a list of resolution -> bitrates somehow ?