New media dependencies have apparently been placed under gst-plugins-meta, which needs to be emerged to pull in packages on which mythtv depends. Add this to package.use:
# MDM mythtv is not finding libFLAC.so.7, looks like I need these now... [flac] [mythtv]
media-plugins/gst-plugins-meta X a52 alsa dvd esd mad mpeg ogg vorbis xv ffmpeg flac mythtv
