playing mp4 files downloaded with getiplayer on blu ray player

[Christopher Woods (CustomMade)]

>  hi
>  I changed the file extension from mp4 to avi .  After 
> burning to dvd when playing on philipps blu ray player video 
> is ok but i get no sound( unsupported  audio format) I get 
> the same  if I leave the mp4 extension untouched  any 
> solutions for the audio?
>  thank you
> cc

Which model number of player do you have? Have you tried renaming to .mov?