Buffering issue (again)

So, after the latest update I sill have buffering issues. I’m getting the “buffering” message just about once every minute or so, and the message “you network might not be fast…” every now and then. It happens with a .m4v file on only 500 MB and a total playing time of over 90 minutes. Does this mean that my network can’t transfer a 500 MB of data in a hour and a half? Most of my .mkv files are HD movies of around 6-7 GB, and those play fine (although sometimes I have issues with them as well). Any ideas?

mkv files buffer endlessly for me for some reason.  Everything else works fine.