Libav is a friendly and community-driven effort to provide its 
users with a set of portable, functional and high-performance 
libraries for dealing with multimedia formats of all sorts. It 
originates from the FFmpeg codebase, but goes its own way these 
days, providing its users with reliable releases and a clear 
vision how to go forward.

Libav enable features (optional) with passing variables to the
script VARIABLE=yes|no ./libav.SlackBuild:

FREI0R=yes|no (default: no), requires frei0r
BS2B=yes|no (default: no), requires libbs2b
DC1394=yes|no (default: no), requires libdc1394
FAAC=yes|no (default: no), requires faac
FDK_ACC=yes|no (default: no), requires libfdk-aac
ILBC=yes|no (default: no), requires libilbc
LAME=yes|no (default: no), requires lame
OPENCORE=yes|no (default: no), requires opencore-amr
OPENCV=yes|no (default: no), requires opencv
OPENJPEG=yes|no (default: no), requires openjpeg
OPUS=yes|no (default: no), requires opus
PULSEAUDIO=yes|no (default: no), requires pulseaudio
RTMP=yes|no (default: no), requires rtmpdump
SCHROEDINGER=yes|no (default: no), requires schroedinger
SPEEX=yes|no (default: no), requires speex
TWOLAME=yes|no (default: no), requires twolame
VPX=yes|no (default: no), requires libvpx
WEBP=yes|no (default: no), requires libwebp
X264=yes|no (default: no), requires x264
X265=yes|no (default: no), requires x265
XIV=yes|no (default: no), requires xvidcore

All features are available from SlackBuilds.org repository.

NOTE: This package conflict with ffmpeg. Do not install both.
