See the update guide and about activating the "Canonical Partners" repo!:
Then try installing the package again!:
sudo apt-get update && sudo apt-get install libavcodec-extra libavcodec-ffmpeg-extra56 mencoder
See the update guide and about activating the "Canonical Partners" repo!:
Then try installing the package again!:
sudo apt-get update && sudo apt-get install libavcodec-extra libavcodec-ffmpeg-extra56 mencoder