[Mark Bowes] “until recently we shot on the Mk3 1080/25fps and it ran perfect, “
Well, of course. It’s 1080, not 4K. That’s not at all an apt comparison.
[Mark Bowes] “4k, 25fps i think its the Dual AMD FirePro D300 “
Decoding 4K will take a lot of power, and you opted for the lowest end GPU.
[Mark Bowes] “if not Proress, what would be a good codec to transcode to ? any advice more than welcome 🙂
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You should make proxies and edit with an offline/online workflow.