FFmpeg is a complete solution to record, convert and stream audio
and video. It includes libavcodec, the leading audio/video codec
library.

You can enable a lot of optional (not-autodetected) features by
passing variables to the script (VAR=yes/no ./ffmpeg.SlackBuild):
AMRNB=yes|no (default: no), requires amrnb (creates non-redistributable binary)
AMRWB=yes|no (default: no), requires amrwb (creates non-redistributable binary)
DC1394=yes|no (default: no), requires libdc1394
DIRAC=yes|no (default: no), requires dirac
FAAC=yes|no (default: yes), requires faac (creates non-redistributable binary)
FAAD=yes|no (default: yes), requires faad2
JP2=yes|no (default: no), requires openjpeg
LAME=yes|no (default: yes), requires lame
OPENCORE=yes|no (default: no), requires opencore-amr
SCHROEDINGER=yes|no (default: no), requires schroedinger
SPEEX=yes|no (default: no), requires speex
VDPAU=yes|no (default: no), requires libvdpau and vdpau capable gpu
X264=yes|no (default: yes), requires x264
XVID=yes|no (default: no), requires xvidcore

ffmpeg is built with runtime cpu detection by default, which might
have a quite big impact on performance. You can turn it off by passing
RUNTIME=no to the script, but this creates a non-portable binary.

All of the mentioned requirements are available from SlackBuilds.org