I've recently got the Tab 3 and love it. Only problem at the moment is MP4 playback. I have MP4 files that plays on my PC (VLC) and plays on my S4 (VLC) but it does not play on my Tab (also VLC)... I've tried about 8 movie players and all have the same problem. All my other MP4 files work on all my devices.
Out of ideas.