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• images->video->web canvas : RGB/YUV issues

  5 février 2016, par nrob

  We’ve written an web app which :

  1. takes 3D, time dependent weather data
  2. tiles each 3D time point to make a 2D frame (written out as a png image)
  3. stitches these frames together into a video (using ffmpeg/avconv)
  4. streams this video into a web app
  5. polls the canvas for frames
  6. sends the frames to the GPU where they are converted back to 3D and ray traced

  You can see the app here, code here and you can see the data video here

  Currently the pngs are written as RGB images, the video codec is in YUV and getting frames from the canvas returns RGB. As such there is a significant loss of information due to the conversion between image spaces.

  Does anyone have suggestions what is the best way round this ?

  I’ve tried a bunch of RGB video codecs, but I can’t get any to work, and I don’t know if the web browser will support it anyway. Can anyone suggest a good RGB codec (both lossy and lossless would be great)

  Also, is it possible to write to YUV images/read them from a video canvas in HTML5 ?

  Ultimately, I don’t even want anything to do with images/videos, I’m just hacking the codecs to stream/compress large animated 3D data volumes

• af_pan : avoid spaces before % to avoid possible issues with MSVC

  12 avril 2013, par Michael Niedermayer

  af_pan : avoid spaces before % to avoid possible issues with MSVC

• PHP exec is causing issues in my webservice

  11 novembre 2013, par meda

  Guys I need some help with this

  I am building an android app that uploads a sound file to a server then converts it.
  Then the next step in my app is to populate a spinner using JSON from another script

  Everything works as expected but for some reason I get an JSON parsing error on the next step.
  I made sure the JSON is correct, so the problem is not there.
  You can trust me on that, I debugged this.

  The android error is :

  E/JSON Parser(14625) : Error parsing data org.json.JSONException : Value
   !DOCTYPE of type java.lang.String cannot be converted to JSONObject

  It the JSON script is not even called, because I put some logs to make sure

  It seems like the issue is comming from the webservice instead, particularly the following function

  function ConvertFileToUlaw($input, $output) { 
  
      try {
  
          exec("ffmpeg -i \"$input\" -codec:a pcm_mulaw -f mulaw \"$output\"");
  
         //error_log($output);
  
      } 
  
      catch (Exception $e) {
  
          error_log($e->getMessage());
  
      }
  
  } 

  I call it like this :

  ConvertFileToUlaw($ThreeGpFilePath, $ulawFilePath);

  Now this works fine, and my sound file is converted, but I can get the next script to run without error, unless I comment it out.

  I am stumped at this point, please advice.