open synaptic (check that universe & multiverse Repositories are enabled) and install the packages:
libavcodec-unstripped-51
libavdevice-unstripped-52
libavformat-unstripped-52
libavutil-unstripped-49
libpostproc-unstripped-51
libswscale-unstripped-0

those are builds with enabled codecs that might have patent problems in some parts of the world, which can't be shipped in the main ubuntu Repos (hence they are published in the multiverse Section). This packages will replace the "usual" builds, and after that the ubuntu vlc build worked to stream video with knots.