convert ogg to mp3 by avconv on Debian Linux

The simple and naive command, which I think, be fitted to almost all situation, is

 avconv -i input.ogg output.mp3

, because of its man page as follows:

     By default avconv tries to pick the "best" stream of each type present in input
       files and add them to each output file. For video, this means the highest
       resolution, for audio the highest channel count. For subtitle it's simply the
       first subtitle stream.

ffmpeg will be discarded soon.