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• Advice with ffmpeg creating clips out of a video

  5 décembre 2016, par Janx from Venezuela

  First of all I’m pretty new at this of video transcoding. I’m trying to use ffmpeg to create a 10 second clip out of a much larger video source, all this in a Node.js application using fluent-ffmpeg. My code goes something like :

  var command = ffmpeg().input(<sourcepath>).native().seekInput(<desiredstartpoint>)
  
      .duration(10)
  
      .on('start', function(commandLine){ // do some database persistence 
  
      }).on('progress',function(e){ // refresh a kill timeout
  
      }).on('error',function(e){ // clean up the mess
  
      }).on('end',function(e){ // success 
  
      }).save(<clipdestinationpath>);
  
  </clipdestinationpath></desiredstartpoint></sourcepath>

  Which usually translates into something like :

    ffmpeg -re -ss <desiredstartpoint> -i <sourcepath> -y -t 10 <clipdestinationpath>
  
  </clipdestinationpath></sourcepath></desiredstartpoint>

  What’s happening is that sometimes the process seems to ’hang’ and I have to manually kill the ffmpeg process (a batch console that appears on windows) for the node process to continue and the ’error’ callback to trigger. Same happens if I run the ffmpeg command manually on a CMD. It usually starts to :

     frame= xxx fps= yy q=x.x size= xxxKb time=00:00:0x.xx bitrate=xx.xxkbits/s
  
     frame= xxx fps= yy q=x.x size= xxxKb time=00:00:0x.xx bitrate=xx.xxkbits/s
  
     frame= xxx fps= yy q=x.x size= xxxKb time=00:00:0x.xx bitrate=xx.xxkbits/s

  Until is suddenly does it no more, and its hanged.

  I do have some fail-overs :

  • On the progress callback, I keep track of a timeout kill action, for when it hangs up, if there’s more than N seconds without activity, I call the kill like

    command.kill();

  • The other thing that I do is to decrement the desiredStartPoint by one (1) second at the time for up to five (5) seconds (greater than zero of course), and try again. Eventually the clip generates right, but it is so random... Sometimes it works like a charm, on the very first (1st) try it creates the clip all is OK to go.

  So my question is :

  • Do you see anything here that I might be missing ? Do I have to consider other variables ? like keyframes, fps, advanced stuffs like that ?

  I’ve also noticed that this happens more frequently on video sources recorded at high bitrate frequencies... I really don’t know men.

• configure : fix linking with MSVC when using —disable-optimizations

  15 décembre 2016, par Steve Lhomme

  configure : fix linking with MSVC when using —disable-optimizations
  Without any optimization flags, MSVC does no dead code elimination (DCE) at
  
  all, even for the most trivial cases. DCE is a prerequisite for building libav
  
  correctly, otherwise there are undefined references to functions for other
  
  architectures and disabled components.
   O1 is the minimal optimization flag for MSVC that does include DCE.
  

  • [DBH] configure

• Trouble understanding XHR streams and express

  17 janvier 2017, par Jon

  I’m having some trouble understanding how I can trigger an XHR response from an express server res.write.

  I’m creating a request on the client with the following code :

   var xhr = new XMLHttpRequest();
  
  
  
   xhr.open(opts.method || 'get', url);
  
  
  
   for (var k in opts.headers||{}) {
  
     xhr.setRequestHeader(k, opts.headers[k]);
  
   }
  
  
  
   xhr.onload = e => res(e.target.responseText);
  
   xhr.onerror = rej;
  
  
  
   if (xhr.upload && progressCb) {
  
     xhr.upload.onprogress = progressCb;
  
   }
  
  
  
   xhr.send(opts.body);

  On the node server, I’m doing multiple res.write() in response to this request.

  For example, I’m creating a video using ffmpeg() and throughout the creation process, I’ll res.write() a JSON.stringified status update.

  The client will receive the last .write(), but the xhr.upload.onprogress callback is not triggered, so I don’t think I understand how to use it correctly. I’m guessing that the xhr.upload.onprogress is meant solely for callbacks related to uploading data to the server, not for triggering a response to multiple writes

  Is there a way for an XHR request to fire a callback every time it receives a res.write() from express ? If not, what’s a better way of achieving this goal ?