I just installed Ubuntu 18.04 along with the restricted extras. I've also installed virtually all the GStream packages in an attempt to fix this problem. Whenever I try to play an mp4 I get a mixture of psychedelic colors. I can make out movement in the videos, but I cannot discern features. I do not have this problem with another Linux I installed.
My computer runs an AMD processor with R7 Radeon graphics.
Thanks for any help you can give.