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• Video Conferencing in HTML5 : WebRTC via Socket.io

  
  1er janvier 2014, par silvia

  Six months ago I experimented with Web sockets for WebRTC and the early implementations of PeerConnection in Chrome. Last week I gave a presentation about WebRTC at Linux.conf.au, so it was time to update that codebase.

  I decided to use socket.io for the signalling following the idea of Luc, which made the server code even smaller and reduced it to a mere reflector :

   var app = require(’http’).createServer().listen(1337) ;
   var io = require(’socket.io’).listen(app) ;
   io.sockets.on(’connection’, function(socket) 
  
           socket.on(’message’, function(message) 
  
           socket.broadcast.emit(’message’, message) ;
  
       ) ;
  
   ) ;
  

  Then I turned to the client code. I was surprised to see the massive changes that PeerConnection has gone through. Check out my slide deck to see the different components that are now necessary to create a PeerConnection.

  I was particularly surprised to see the SDP object now fully exposed to JavaScript and thus the ability to manipulate it directly rather than through some API. This allows Web developers to manipulate the type of session that they are asking the browsers to set up. I can imaging e.g. if they have support for a video codec in JavaScript that the browser does not provide built-in, they can add that codec to the set of choices to be offered to the peer. While it is flexible, I am concerned if this might create more problems than it solves. I guess we’ll have to wait and see.

  I was also surprised by the need to use ICE, even though in my experiment I got away with an empty list of ICE servers – the ICE messages just got exchanged through the socket.io server. I am not sure whether this is a bug, but I was very happy about it because it meant I could run the whole demo on a completely separate network from the Internet.

  The most exciting news since my talk is that Mozilla and Google have managed to get a PeerConnection working between Firefox and Chrome – this is the first cross-browser video conference call without a plugin ! The code differences are minor.

  Since the specification of the WebRTC API and of the MediaStream API are now official Working Drafts at the W3C, I expect other browsers will follow. I am also looking forward to the possibilities of :

  • multi-peer video conferencing like the efforts around webrtc.io,
  • the media stream recording API,
  • and the peer-to-peer data API.

  The best places to learn about the latest possibilities of WebRTC are webrtc.org and the W3C WebRTC WG. code.google.com has open source code that continues to be updated to the latest released and interoperable features in browsers.

  The video of my talk is in the process of being published. There is a MP4 version on the Linux Australia mirror server, but I expect it will be published properly soon. I will update the blog post when that happens.

• How do I use ffmpeg4android in an ADT project ?

  16 janvier 2013, par mystafer

  I used the project FFmpeg4Android on sourceforge to build the FFmpeg .so shared library files. However, I am having trouble using them in an ADT Java application. I created a simple JNI call that attempts to call av_register_all and I get library errors.

  When I run the application on my Nexus 7 I am told that it is unable to load library libavformat-HEAD-1.0.so

  So I tried to load this via the System.loadLibrary method and I was unable to find libavcodec-HEAD-1.0.so. Working my way back in this manner I eventually attempted to load libavutil-HEAD-1.0.so which yielded an error 'cannot locate symbol "__strchr_chk"'.

  This is my Java class :

  public class LibavcodecTest {
  
      public static native void avRegisterAll();
  
  
  
      static {
  
          System.loadLibrary("avutil-HEAD-1.0");
  
          System.loadLibrary("avcodec-HEAD-1.0");
  
          System.loadLibrary("avformat-HEAD-1.0");
  
          System.loadLibrary("LibavcodecTest");
  
      }
  
  }

  Update

  I contacted the developer that maintains ffmpeg4android and he was able to direct me to change the version of the android source I was building against to the same as my device which worked to allow my to call av_register_all successfully.

  However, now I get a crash calling avformat_open_input where I receive "Fatal signal 11 (SIGSEGV)".

  My search on the web makes me believe this is a memory access issue. Does anybody know if this may be resolved by loading the shared libraries differently ?

• Rotate mp4 videos without re-encoding

  3 novembre 2015, par stedes

  I’m looking for a way to rotate videos shot with my Nexus 4 on my Debian Wheezy sytem. The videos are shot in portrait mode and I would like to rotate them to landscape mode. Preferably the rotation is command-line driven.

  I have found several previous questions which are hinting at a good solution but I can’t seem to manage to get it working.

  To begin with there was this question :
  Rotating videos with FFmpeg

  But it indicates that ffmpeg is outdated and that I should use avconv. I found this question detailing the way to go forward.
  http://askubuntu.com/questions/269429/how-can-i-rotate-video-by-180-degrees-with-avconv

  This made me using following command :

  avconv -i original.mp4 -vf "transpose=1" -codec:v libx264 -preset slow -crf 25 -codec:a copy flipped.mp4

  However, this is painstakingly slow (last test took me more than 6 hours for less than 3 minutes of footage) and does not result in a playable movie. I also get an error in logging output which states Mb Rate > level limit.

  Is there an issue here with the re-encoding ? Should I first re-encode the videos from my phone to another, more "workable" encoding before applying the rotations ? Or am I missing another important point ?

  Thanks in advance