SlackBuildsOrg/multimedia/ffmpeg

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):
ASS=yes|no (default: no), requires libass
BLURAY=yes|no (default: no), requires libbluray
CELT=yes|no (default: no), requires celt
DC1394=yes|no (default: no), requires libdc1394
FAAC=yes|no (default: no), requires faac (creates non-redistributable binary)
FREI0R=yes|no (default: no), requires frei0r
GSM=yes|no (default: no), requires gsm
IEC61883=yes|no (default: no), requires libiec61883 and libavc1394
ILBC=yes|no (default: no), requires libilbc
JP2=yes|no (default: no), requires openjpeg
LADSPA=yes|no (default: no), requires ladspa_sdk
LAME=yes|no (default: yes), requires lame
MODPLUG=yes|no (default: no), requires libmodplug
OPENAL=yes|no (default: no), requires OpenAL
OPENCORE=yes|no (default: no), requires opencore-amr
OPENSSL=yes|no (default: no), creates non-redistributable binary
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
X264=yes|no (default: yes), requires x264
XVID=yes|no (default: no), requires xvidcore

Make sure to run this script in a real root shell ("su -") and that you
have either tetex or texlive installed.

All of the mentioned requirements are available from SlackBuilds.org