My TV has USB sockets. Amongst various other formats, the manual says it can play some MP4 files, in particular ones created by Panasonic equipment. I had only minor (and varied) successes using my existing codecs. And my 5 year old Codec from Divx produced dreadful 1280*720 files and unplayable 1920*1080 files.
The good news is that the TV is certified to accept "DivX Plus HD" files. So, for £25, I purchased the up to date pack from DivX. Wonderful! All my tests have worked (so far). I can now watch my lousy clips on a big screen.
I assume the media playing capabilities of future TVs will accept even wider ranges of codecs. In the meantime, well done Panasonic and DivX.