Upstream is using transcode, but gentoo package has patch to force ffmpeg: http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/media-video/ttcut/files/ttcut-0.19.6-ffmpeg-vf-setdar.patch?view=log
The patch for ffmpeg was introduced because it is still in development unlike transcode. Ttcut is not developed for quite a while as well but like backlite I would like to keep it as long as possible.
+ 01 Mar 2014; Daniel Pielmeier <billie@gentoo.org> ttcut-0.19.6-r3.ebuild: + Depend on media-video/ffmpeg instead of virtual/ffmpeg. See bug #474348.