Joining 2 videos in Ubuntu

sudo apt-get install mencoder

cat video1.mpg video2.mpg > video12.mpg

Rip video or audio from Youtube video

# Install youtube-dl to download video into flv file
sudo apt-get install youtube-dl
youtube-dl http://

# Install ffmpeg to do the conversions
sudo apt-get install ffmpeg

# Convert to mp3 audio
sudo apt-get install libavcodec-unstripped-52
ffmpeg -i input.flv -ac 2 -ab 128000 -ar 44100 output.mp3

# Convert to mpeg video
ffmpeg -i input.flv output.mpg

refs:
http://pblog.ebaker.me.uk/2009/01/rip-youtube-videos-on-ubuntu.html
https://lists.ubuntu.com/archives/universe-bugs/2009-January/041895.html