IPTV mp4 VODs won't load


My IPTV live channels work fine, however I also have VODs & series that have a .mp4 extension (I believe they are h.264 AVC (part 10)).
When I try to play them, they either hang on a black screen & say "preparing..." OR I get an instant "channel format not supported".

I'm using ProgDVB Standard Edition x64 7.47.09.
The codec set for h.264/AVC is LAV Video Decoder, however I have tried Elecard AVC Video Decoder & it still doesn't work.

Note: This problem doesn't exist for me in VLC player, they load fine.