Since no TV station or channel broadcasts in mpeg4 I would have to guess there is not a TV Channel involved at all but some file in mpeg4 format that doesn't play.
Let's lead with this. If it doesn't play then the encoding is not supported. There are long discussions about encoding so I won't repeat that here but point to any manual and see what is supported.
I have a Samsung series 6 TV, Model LE40A656A, and I can't watch a TV Chanel in format HD 'mpeg4'.
I need a solution.