Bonjour sjox,
It is not a salix error, all these codecs are deactivated in the Slackware 15.0 FFMPEG build currently
libx264="" ; [ "${X264:-no}" != "no" ] && libx264="--enable-libx264"
libcelt="" ; [ "${CELT:-no}" != "no" ] && libcelt="--enable-libcelt"
libdc1394="" ; [ "${DC1394:-no}" != "no" ] && libdc1394="--enable-libdc1394"
libgsm="" ; [ "${GSM:-no}" != "no" ] && libgsm="--enable-libgsm"
librtmp="" ; [ "${RTMP:-no}" != "no" ] && librtmp="--enable-librtmp"
libxvid="" ; [ "${XVID:-no}" != "no" ] && libxvid="--enable-libxvid"
libass="" ; [ "${ASS:-no}" != "no" ] && libass="--enable-libass"
libiec61883=""; [ "${IEC61883:-no}" != "no" ] && libiec61883="--enable-libiec61883"
libilbc="" ; [ "${ILBC:-no}" != "no" ] && libilbc="--enable-libilbc"
libmodplug="" ; [ "${MODPLUG:-no}" != "no" ] && libmodplug="--enable-libmodplug"
libtwolame="" ; [ "${TWOLAME:-no}" != "no" ] && libtwolame="--enable-libtwolame"
ladspa="" ; [ "${LADSPA:-no}" != "no" ] && ladspa="--enable-ladspa"
libflite="" ; [ "${FLITE:-no}" != "no" ] && libflite="--enable-libflite"
libx265="" ; [ "${X265:-no}" != "no" ] && libx265="--enable-libx265"
libzvbi="" ; [ "${ZVBI:-no}" != "no" ] && libzvbi="--enable-libzvbi"
libopencv="" ; [ "${OPENCV:-no}" != "no" ] && libopencv="--enable-libopencv"
libgme="" ; [ "${GME:-no}" != "no" ] && libgme="--enable-libgme"
libsnappy="" ; [ "${SNAPPY:-no}" != "no" ] && libsnappy="--enable-libsnappy"
libzmq="" ; [ "${ZMQ:-no}" != "no" ] && libzmq="--enable-libzmq"
libbs2b="" ; [ "${BS2B:-no}" != "no" ] && libbs2b="--enable-libbs2b"
rubberband="" ; [ "${RUBBERBAND:-no}" != "no" ] && rubberband="--enable-librubberband"
tesseract="" ; [ "${TESSERACT:-no}" != "no" ] && tesseract="--enable-libtesseract"
libjack="" ; [ "${JACK:-no}" != "no" ] && libjack="--enable-libjack"
libaom="" ; [ "${AOM:-no}" != "no" ] && libaom="--enable-libaom"
lv2="" ; [ "${LV2:-no}" != "no" ] && lv2="--enable-lv2"
libdav1d="" ; [ "${DAV1D:-no}" != "no" ] && libdav1d="--enable-libdav1d"
rabbitmq="" ; [ "${RABBITMQ:-no}" != "no" ] && rabbitmq="--enable-librabbitmq"
libcodec2="" ; [ "${CODEC2:-no}" != "no" ] && libcodec2="--enable-libcodec2"
libsoxr="" ; [ "${SOXR:-no}" != "no" ] && libsoxr="--enable-libsoxr"
libsrt="" ; [ "${SRT:-no}" != "no" ] && libsrt="--enable-libsrt"
libzimg="" ; [ "${ZIMG:-no}" != "no" ] && libzimg="--enable-libzimg"
chromaprint="" ; [ "${CHROMAPRINT:-no}" != "no" ] && chromaprint="--enable-chromaprint"
vapoursynth="" ; [ "${VAPOURSYNTH:-no}" != "no" ] && vapoursynth="--enable-vapoursynth"
opencore_amr="" ; [ "${OPENCORE:-no}" != "no" ] && \