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brado Which GPU do you have? Does your CPU have an integrated GPU?
Which video output is your primary screen plugged in to? The GPU card or the one on motherboard?
With klite/LAV intalled, go to start and type LAV and open the app. Can you try setting it to copyback and have your GPUcard selected (must be primary display attached to too.) Depending on which GPU you have you may try other Decoders too. But Copy-back is in most cases best performance.
D3D11 works quite well too on newer gen GPU's
In the Formats tab (on top left), see if H.264, mpeg-4 part 2 and hevc are checked on.