Hi in ubuntu you can able to convert flv file to mpg.first download the file from youtube or if u are going to view the file in youtube,the file will be stored in the temp directory so copy the file from the tem to ur home directory.
Now install ffmpeg .Go to ur terminal and type sudo apt get install ffmpeg.
Now ffmpeg was installed.now u use this command in the terminal as
ffmpeg -i gen -ab 56 -ar 22050 -b 500 -s 320x240 test.mpg
here gen is flv file name and test.mpg is the name which you want to have it in mpg.
The script, in this order:
1. Launches FFMPEG
2. Opens your FLV (change to suit yours)
3. -ab : Sets the audio bitrate. Without this, it’ll be set to the default of 64kbps
4. -ar : Sets the audio samplerate. Default is 44100hz
5. -b : Sets the video bitrate. Default is 2000kbps
6. -s : Sets the size. Default is 160×128px
7. Outputs to the filename you enter (change to suit your needs)