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

Calculating dependencies ... done!
Dependency resolution took 0.98 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/utfcpp-4.0.6::gentoo  USE="-test" 34 KiB
[ebuild  N     ] dev-libs/libebml-1.4.7:0/5::gentoo  USE="-verify-sig" 51 KiB
[ebuild  N     ] media-libs/libmatroska-1.7.2:0/7::gentoo  USE="-verify-sig" 62 KiB

Total: 3 packages (3 new), Size of downloads: 145 KiB