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• Tainted canvas may not be exported. When trying to send it via ajax to php file

  6 décembre 2015, par romikette F

  I am trying to capture an image from a local video so I can make a thumb out of it. I am trying to avoid using video conversions (like ffmpeg) to save server resources and keep my videos in theyr original format.
  I’we been reading about tainted canvases and I understand I am trying to breach the browsers security protocols. But this article https://developer.mozilla.org/en-US/docs/Web/HTML/CORS_enabled_image#What_is_a_tainted_canvas said that I could pull an image if it were from a different source (something something).
  So far I have this :

  <video src="http://www.w3schools.com/html/mov_bbb.mp4" type="video/mp4" controls="controls"></video><br />
  
  <button>Capture</button> <br /><br />
  
  <div></div>
  
  <canvas></canvas> <br /><br />

  and :

  function capture(){
  
  var canvas = document.getElementById('mYcanvas');
  
  var video = document.getElementById('video');
  
  canvas.getContext('2d').drawImage(video, 0, 0, video.videoWidth, video.videoHeight);
  
  
  
  function getBase64() {
  
  var img = document.getElementById("mYcanvas");
  
  var canvas = document.createElement("canvas");
  
  canvas.width = img.width;
  
  canvas.height = img.width;
  
  var ctx = canvas.getContext("2d");
  
  ctx.drawImage(img, 0, 0);
  
  var dataURL = canvas.toDataURL("image/png");
  
  alert(dataURL.replace(/^data:image\/(png|jpg);base64,/, "")); 
  
  
  
  $.ajax({
  
      url: 'submit_image.php',
  
      type: 'POST',
  
      data: {
  
          imgdata: dataURL
  
      },
  
      success: function (res) {
  
              document.getElementById("response").innerHTML = res;
  
          }
  
  });
  
  }
  
  getBase64();
  
  
  
  }

  Never mind the php. It dose not receive anything.

• Web script can't find installed package/software (CentOS)

  14 janvier 2017, par Ryan Butterworth

  I’m pretty new to using SSH and such to install software. I’m trying to use https://github.com/eyecatchup/php-yt_downloader on my site (http://voddr.com/yt/index.php?id=yrreBFLghMc) but as you can see, it comes back with the error "You must have Ffmpeg installed in order to use this function."

  I have installed ffmpeg, using Nux Desktop (see the guide I followed here : https://www.vultr.com/docs/how-to-install-ffmpeg-on-centos)

  When typing "ffmpeg" into SSH it comes back with this, which must mean it is installed :

  

  Also, I tried the command "which ffmpeg", which returned the path of ffmpeg : "/usr/bin/ffmpeg"

  php-yt_downloader uses which ffmpeg to detect whether it is installed, and if not, it returns the error "You must have Ffmpeg installed in order to use this function." - but if I’m able to use it fine from my SSH window, why can’t the script detect it ?

  All I’m wondering, is there something else I must do when installing software to allow a domain to use it (like install the software in the domain’s path ?), or is this entirely a problem with the php-yt_downloader resource ? I’m using CentOS 7 and Plesk web panel.

• RAR Is Still A Contender

  31 mai 2012, par Multimedia Mike — Science Projects, bzip2, compression, gzip, lossless, rar, xz

  RAR (Roshal ARchive) is still a popular format in some corners of the internet. In fact, I procured a set of nearly 1500 RAR files that I want to use in a little project. But I didn’t want my program to have to operate directly on the RAR files which meant that I would need to recompress them to another format. Surely, one of the usual lossless compressors commonplace with Linux these days would perform better. Probably not gzip. Maybe not bzip2 either. Perhaps xz, though ?

  Conclusion
  At first, I concluded that xz beat RAR on every single file in the corpus. But then I studied the comparison again and realized it wasn’t quite apples to apples. So I designed a new experiment.

  New conclusion : RAR still beats xz on every sample in this corpus (for the record, the data could be described as executable program data mixed with reduced quality PCM audio samples).

  Methodology
  My experiment involved first reprocessing the archive files into a new resource archive file format and only compressing that file (rather than a set of files) using gzip, bzip2, xz, and rar at the maximum compression settings.

  echo filesize,gzip,bzip2,xz,rar,filename > compressed-sizes.csv
  for f in `ls /path/to/files/*`
  do
    gzip -9 —stdout $f > out.gz
    bzip2 -9 —stdout $f > out.bz2
    xz -9 —stdout —check=crc32 $f > out.xz
    rar a -m5 out.rar $f
    stat —printf "%s," $f out.gz out.bz2 out.rar out.xz >> compressed-sizes.csv
    echo $f >> compressed-sizes.csv
    rm -f out.gz out.bz2 out.xz out.rar
  done
  

  Note that xz gets the option '--check=crc32' since I’m using the XZ Embedded library which requires it. It really doesn’t make a huge different in filesize.

  Experimental Results
  The preceding command line generates compressed-sizes.csv which goes into a Google Spreadsheet (export as CSV).

  Here are the full results of the bake-off, graphed :

  
  
  

  That’s not especially useful. Here are the top 2 contenders compared directly :

  
  
  

  Action
  Obviously, I’m unmoved by the data. There is no way I’m leaving these files in their RAR form for this project, marginal space and bandwidth savings be darned. There are other trade-offs in play here. I know there is free source code available for decompressing RAR files but the license wouldn’t mesh well with GPL source code libraries that form the core of the same project. Plus, the XZ Embedded code is already integrated and painstakingly debugged.

  During this little exercise, I learned of a little site called Maximum Compression which takes experiments like the foregoing to their logical conclusion by comparing over 200 compression programs on a standard data corpus. According to the site’s summary page, there’s a library called PAQ8PX which posts the best overall scores.