Couple days ago I encountered an audio conversion failed: Unknown encoder ‘libmp3lame’ error when I tried to convert YouTube videos to mp3 format using youtube-dl.
$ youtube-dl --extract-audio --audio-format=mp3 -t https://www.youtube.com/... [youtube] Setting language [youtube] PL: Downloading page #1 [youtube] xxx: Downloading video webpage [youtube] xxx: Downloading video info webpage [youtube] xxx: Extracting video information [download] Destination: xxx.flv [download] 100.0% of 9.54M at 105.96k/s ETA 00:00 [ffmpeg] Destination: xxx.mp3 ERROR: audio conversion failed: Unknown encoder 'libmp3lame'
Hopefully this problem is answered at the answers.launchpad.net (Error extracting audio to mp3).
Quick solutions is to install libavcodec-extra-53 package:
$ sudo apt-get install libavcodec-extra-53