Enoch

have you tried viewing it on a different computer? the 4k files are pretty memory/graphics card intensive. especially if you are at 400mbps a sec. when i try to view it on an older macbook air it definitely stutters and stalls out, but it works fine when view it on a MacBook pro. out of curiosity, are you in the UK? it is unusual to shoot in 25p, usually shoot in 24, 30 or 60p in the states. also you might want to shoot in drop frame as that converts better for actual tv, streaming or broadcast, that would be 23.976, 29.97 or 59.94p.