These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.52 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/libunibreak-8.0:0/8::gentoo  USE="-doc -man -static-libs -test" 1063 KiB
[ebuild  N     ] media-libs/alsa-topology-conf-1.2.5.1-r1::gentoo  USE="-verify-sig" 12 KiB
[ebuild  N     ] media-libs/alsa-ucm-conf-1.2.16.1::gentoo  USE="-verify-sig" 83 KiB
[ebuild  N     ] dev-build/b2-5.5.3::gentoo  USE="-examples" 1198 KiB
[ebuild  N     ] app-text/pandoc-bin-3.12.1::gentoo  USE="pandoc-symlink" 34535 KiB
[ebuild  N     ] dev-libs/xerces-c-3.3.0-r1:0/3.3::gentoo  USE="iconv icu -curl -doc -examples -static-libs -test" CPU_FLAGS_X86="sse2" 4211 KiB
[ebuild  N     ] media-libs/alsa-lib-1.2.16.1::gentoo  USE="python -debug -doc -verify-sig" PYTHON_SINGLE_TARGET="python3_14 -python3_12 -python3_13 (-python3_15)" 1104 KiB
[ebuild  N     ] dev-cpp/valijson-1.1.3::gentoo  745 KiB
[ebuild  N     ] media-libs/dav1d-1.5.4:0/7::gentoo  USE="8bit 10bit asm -test -xxhash" 1015 KiB
[ebuild  N     ] media-libs/x264-0.0.20240513-r1:0/164::gentoo  USE="interlaced -opencl -static-libs" 822 KiB
[ebuild  N     ] media-libs/x265-4.3:0/217::gentoo  USE="10bit 12bit cet -numa -test -vmaf" 2005 KiB
[ebuild  N     ] media-libs/xvid-1.3.7-r2::gentoo  USE="-examples" 683 KiB
[ebuild  N     ] dev-libs/double-conversion-3.4.0:0/3::gentoo  USE="-test" 6871 KiB
[ebuild  N     ] dev-libs/md4c-0.6.0::gentoo  USE="md2html -test" 263 KiB
[ebuild  N     ] sys-libs/mtdev-1.1.7::gentoo  295 KiB
[ebuild  N     ] x11-misc/xkeyboard-config-2.48::gentoo  USE="-test" 931 KiB
[ebuild  N     ] virtual/pandoc-0-r1::gentoo  0 KiB
[ebuild  N     ] x11-libs/xcb-util-renderutil-0.3.10::gentoo  256 KiB
[ebuild  N     ] dev-libs/boost-1.91.0-r2:0/1.91.0::gentoo  USE="bzip2 context nls python stacktrace zlib -debug -doc -icu -lzma -mpi -numpy -test -test-full -tools -zstd" PYTHON_TARGETS="python3_14 -python3_12 -python3_13" 199785 KiB
[ebuild  N     ] dev-libs/xalan-c-1.12-r4:0/1.12::gentoo  USE="-doc -verify-sig" 1105 KiB
[ebuild  N     ] x11-libs/libXv-1.0.13::gentoo  USE="-doc" 275 KiB
[ebuild  N     ] media-libs/libass-0.17.5-r1:0/9::gentoo  USE="fontconfig libunibreak -test -verify-sig" 450 KiB
[ebuild  N     ] net-libs/libssh-0.12.2:0/4::gentoo  USE="sftp zlib -debug -examples -fido2 -gssapi -mbedtls -pcap -server -static-libs -test -verify-sig" 742 KiB
[ebuild  N     ] x11-libs/libxkbcommon-1.13.2::gentoo  USE="X -doc -static-libs -test -tools -wayland" 1215 KiB
[ebuild  N     ] x11-libs/xcb-util-wm-0.4.2::gentoo  279 KiB
[ebuild  N     ] dev-libs/libevdev-1.13.7::gentoo  USE="-doc -test" 462 KiB
[ebuild  N     ] x11-libs/xcb-util-0.4.1::gentoo  262 KiB
[ebuild  N     ] x11-libs/xcb-util-image-0.4.1::gentoo  283 KiB
[ebuild  N     ] media-video/ffmpeg-8.1.3:0/60.62.62::gentoo  USE="X alsa bzip2 cairo dav1d drm fontconfig gmp gnutls gpl jpeg2k libass opengl openssl ssh truetype x264 x265 xml xvid zlib -amf -amr -amrenc (-appkit) -bluray -bs2b -cdio -chromaprint -chromium -codec2 -cuda-clang -doc -dvd -fdk -flite -frei0r -fribidi -gcrypt -gme -gsm -iec61883 -ieee1394 -jack -jpegxl -kvazaar -ladspa -lame -lcms -libaom -libaribb24 -libcaca -libilbc -liblc3 -libplacebo -librtmp -libsoxr -lv2 -lzma -modplug -nvenc -ocr -openal -opencl -opencolorio -openh264 -openmpt -opus -pulseaudio -qrcode -qsv -quirc -rabbitmq -rav1e -rist -rubberband -samba -sdl -snappy -sndio -soc -sofa -speex -srt -svg -svt-av1 -theora -twolame -v4l -vaapi -vdpau -verify-sig -vidstab -vmaf -vorbis -vpx -vulkan -webp -zeromq -zimg -zvbi" 11458 KiB
[ebuild  N     ] dev-libs/libinput-1.32.0:0/10::gentoo  USE="-doc -lua -test" INPUT_DEVICES="-wacom" LUA_SINGLE_TARGET="lua5-4" 944 KiB
[ebuild  N     ] x11-libs/xcb-util-cursor-0.1.6::gentoo  267 KiB
[ebuild  N     ] dev-qt/qtbase-6.11.2-r2:6/6.11.2::gentoo  USE="X concurrent dbus gui libinput network nls opengl sql sqlite ssl udev widgets xml (zstd) -accessibility -brotli -cups -custom-cflags -eglfs -evdev -gles2-only -gssapi -gtk -icu -io-uring (-journald) -libproxy -mysql -oci8 -odbc -postgres -renderdoc -sctp -syslog -test -tslib -vulkan -wayland" 49398 KiB
[ebuild  N     ] dev-qt/qttools-6.11.2:6/6.11.2::gentoo  USE="assistant linguist opengl qdbus widgets (zstd) -custom-cflags -designer -distancefieldgenerator -gles2-only -kmap2qmap -pixeltool -qdoc -qml -qmlls -qtattributionsscanner -qtdiag -qtplugininfo -vulkan" LLVM_SLOT="22 -17 -18 -19 -20 -21" 9992 KiB
[ebuild  N     ] dev-qt/qttranslations-6.11.2:6/6.11.2::gentoo  USE="-custom-cflags" 1652 KiB
[ebuild  N     ] dev-qt/qtsvg-6.11.2:6/6.11.2::gentoo  USE="-custom-cflags -test" 2287 KiB
[ebuild  N     ] dev-qt/qtshadertools-6.11.2:6/6.11.2::gentoo  USE="-custom-cflags -test" 1189 KiB
[ebuild  N     ] dev-qt/qtmultimedia-6.11.2:6/6.11.2::gentoo  USE="X alsa dbus ffmpeg opengl v4l -custom-cflags -eglfs -gstreamer -pipewire -pulseaudio -qml -test -vaapi -vulkan -wayland" 10015 KiB
[ebuild  N     ] app-misc/brewtarget-4.0.17-r1::gentoo  14165 KiB

Total: 38 packages (38 new), Size of downloads: 362301 KiB

The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by dev-libs/xalan-c-1.12-r4::gentoo
# required by app-misc/brewtarget-4.0.17-r1::gentoo
# required by =app-misc/brewtarget-4.0.17-r1 (argument)
>=dev-libs/xerces-c-3.3.0-r1 icu

 * In order to avoid wasting time, backtracking has terminated early
 * due to the above autounmask change(s). The --autounmask-backtrack=y
 * option can be used to force further backtracking, but there is no
 * guarantee that it will produce a solution.