title: GStreamer - How to compose three streams (two video files with audio)
body: <p>I have two avi files (one contains only video and the second file consists of video and audio stream). I would like to composite/mix two avi files to one video file (side by side) and preserve audio. </p>
  
  <p>I can compose video streams (using videomixer) but I don't know how to add audio stream:<br/>
  <code>
  gst-launch filesrc location=test01.avi ! decodebin ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=640, height=480 ! videobox border-alpha=0 left=-640 ! videomixer name=mix ! ffmpegcolorspace ! queue ! avimux ! filesink location=videoTestMix666.avi filesrc location=test02.avi ! decodebin ! videoscale ! ffmpegcolorspace ! video/x-raw-yuv, width=640, height=480 ! videobox right=-640 ! mix. 
  </code></p>
  
  <p>
  Could you advice me hot to do this - how to add audio? Many thanks
  </p>