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

Calculating dependencies ... done!
Dependency resolution took 1.05 s (backtrack: 0/20).

[ebuild  N     ] media-libs/opus-1.6.1::gentoo  USE="-custom-modes -debug -deep-plc -doc -dred -hardened -osce -static-libs -test" CPU_FLAGS_X86="sse" 10228 KiB
[ebuild  N     ] dev-lang/yasm-1.3.0-r2::gentoo  USE="nls" 1458 KiB
[ebuild  N     ] media-libs/libvpx-1.16.0:0/12::gentoo  USE="highbitdepth -doc -postproc -static-libs -test" 5504 KiB
[ebuild  N     ] net-libs/tox-0.2.23:0/0.2::gentoo  USE="av ipv6 log-error -daemon -debug -dht-node -experimental -key-utils -log-debug -log-info -log-trace -log-warn -test" 989 KiB

Total: 4 packages (4 new), Size of downloads: 18177 KiB