ffmpeg is not in jessie, as Debian had gone the libav way. It's now in unstable and would expect to see it in jessie-backports soon (or we could do it, of course; it should be easy enough). However, I think we depend on libav in other parts of the MW infrastructure and depending on both sounds like a bad idea. We should investigate further.
Some service is relying on ffmpeg (maybe the video thumbnailer). Debian Jessie does not provide ffmpeg but provides libav instead. We need to investigate the impact on our infrastructure and identify software/settings changes that need to be happen to be able to switch.