Well, moomin74, no one seems to be leaping into this fray. I have no familiarity either. However, I notice that https://bbs.deepin.org/module has binaries available, including one specific to Ubuntu Trusty Tahr, the basis for deepin 14. The last binary for Ubuntu I installed was Kodi on TahrPup 6.0.2, and it literally took care of itself. Have you tried asking on the ffmpeg forum? If you can get no joy there, do you have an extra machine for experiments? Failing that, try downloading the TahrPup ISO, burn it to DVD, and boot off that. Once in Puppy, download the Tahr binary from ffmpeg and play with it in RAM. It's a way to experiment off your HD install of deepin. If you reach a comfortable familiarity, burn a second Puppy disk while in Puppy (just take the disk out and but in a blank, navigate to the ISO file on the HD and right click it.) Pburn will offer to burn a multi-session (persistent) disk. Try ffmpeg one more time with this and save the success to the disk. Boot into deepin, use the disk for reference, and go for it. Good luck!

Thanks for your reply. I figured it out with this:

sudo add-apt-repository ppa:mc3man/trusty-media sudo apt-get update sudo apt-get install ffmpeg

Doug McMahon on launchpad.net?