Wrt transcoding: it should be possible to run this stuff HW accelerated on the SoC's video engine of Rockchip boards or Exynos 5422 ODROIDs but I lost track about the progress being made there...
Thanks, hmm, maybe ODROID HC2 is also good choice, I think I can install 2x2.5 HDD in its case. 2nd hdd connect to USB and use for backups.