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• Add multiple audio files to video at specific points using FFMPEG

  7 août 2012, par Pascal Beyeler

  I am trying to create a video out of a sequence of images and various audio files using FFmpeg. While it is no problem to create a video containing the sequence of images with the following command :

  ffmpeg -f image2 -i image%d.jpg video.mpg

  I haven't found a way yet to add audio files at specific points to the generated video.
  Is it possible to do something like :

  ffmpeg -f image2 -i image%d.jpg -i audio1.mp3 AT 10s -i audio2.mp3 AT 15s video.mpg

  Any help is much appreciated !

  EDIT :

  The solution in my case was to use sox as suggested by blahdiblah in the answer below. You first have to create an empty audio file as a starting point like that :

  sox -n -r 44100 -c 2 silence.wav trim 0.0 20.0

  This generates a 20 sec empty WAV file. After that you can mix the empty file with other audio files.

  sox -m silence.wav "|sox sound1.mp3 -p pad 0" "|sox sound2.mp3 -p pad 2" out.wav

  The final audio file has a duration of 20 seconds and plays sound1.mp3 right at the beginning and sound2.mp3 after 2 seconds.
  To combine the sequence of images with the audio file we can use FFmpeg.

  ffmpeg -i video_%05d.png -i out.wav -r 25 out.mp4

• Video Conferencing in HTML5 : WebRTC via Web Sockets

  14 juin 2012, par silvia

  A bit over a week ago I gave a presentation at Web Directions Code 2012 in Melbourne. Maxine and John asked me to speak about something related to HTML5 video, so I went for the new shiny : WebRTC – real-time communication in the browser.

  Presentation slides

  I only had 20 min, so I had to make it tight. I wanted to show off video conferencing without special plugins in Google Chrome in just a few lines of code, as is the promise of WebRTC. To a large extent, I achieved this. But I made some interesting discoveries along the way. Demos are in the slide deck.

  UPDATE : Opera 12 has been released with WebRTC support.

  Housekeeping : if you want to replicate what I have done, you need to install a Google Chrome Web Browser 19+. Then make sure you go to chrome ://flags and activate the MediaStream and PeerConnection experiment(s). Restart your browser and now you can experiment with this feature. Big warning up-front : it’s not production-ready, since there are still changes happening to the spec and there is no compatible implementation by another browser yet.

  Here is a brief summary of the steps involved to set up video conferencing in your browser :

  1. Set up a video element each for the local and the remote video stream.
  2. Grab the local camera and stream it to the first video element.
  3. (*) Establish a connection to another person running the same Web page.
  4. Send the local camera stream on that peer connection.
  5. Accept the remote camera stream into the second video element.

  Now, the most difficult part of all of this – believe it or not – is the signalling part that is required to build the peer connection (marked with (*)). Initially I wanted to run completely without a server and just enter the remote’s IP address to establish the connection. This is, however, not a functionality that the PeerConnection object provides [might this be something to add to the spec ?].

  So, you need a server known to both parties that can provide for the handshake to set up the connection. All the examples that I have seen, such as https://apprtc.appspot.com/, use a channel management server on Google’s appengine. I wanted it all working with HTML5 technology, so I decided to use a Web Socket server instead.

  I implemented my Web Socket server using node.js (code of websocket server). The video conferencing demo is in the slide deck in an iframe – you can also use the stand-alone html page. Works like a treat.

  While it is still using Google’s STUN server to get through NAT, the messaging for setting up the connection is running completely through the Web Socket server. The messages that get exchanged are plain SDP message packets with a session ID. There are OFFER, ANSWER, and OK packets exchanged for each streaming direction. You can see some of it in the below image :

  

  I’m not running a public WebSocket server, so you won’t be able to see this part of the presentation working. But the local loopback video should work.

  At the conference, it all went without a hitch (while the wireless played along). I believe you have to host the WebSocket server on the same machine as the Web page, otherwise it won’t work for security reasons.

  A whole new world of opportunities lies out there when we get the ability to set up video conferencing on every Web page – scary and exciting at the same time !

• How to install FFmpeg on a Linux server using SSH [closed]

  29 janvier 2013, par user2019961

  I've been trying my hardest and I can't seem to find a straight answer ; I have the latest version of FFmpeg downloaded and uploaded to my server, SSH enabled and I can get into the shell command prompt but I can't figure out how to actually install it. IT says just to type ./configure but that does nothing. Can anyone help me to install it ?