*Unset LANG envar for the script execution time, because commands like "apt-cache policy" will return translated messages, which would not be grep'ed crrectly... *Disable using distrib's ffmpeg for DEB distribs too, as e.g. official debian features libav under ffmpeg name, which is not that much compatible with current Blender code. *Also check for libxvidcore-dev .deb package, debian has no libxvidcore4-dev ;)