After upgrading to the recently stabilized =media-video/ffmpeg-3.2.4, "emerge @preserved-rebuild" tried to rebuild =media-sound/moc-2.5.0 (the current stable version), which failed due to a missing header file (specifically: libavutil/audioconvert.h). =media-sound/moc-2.5.2, however, *does* compile and work (from the NEWS file it looks like 2.5.1 introduced the fix), so it would probably be a good idea to stabilize that version along with ffmpeg.
amd64 stable
x86 stable
*** Bug 609546 has been marked as a duplicate of this bug. ***
sparc stable
Stable on alpha.
ppc64 stable
ppc stable. Closing.