How to simultaneously use cpu and igpu for decoding?

[Selur]

I assuming you enabled "Config->Decoding->Use gpu for decoding" with the tool-tip stating:

Use gpu decoding:
When enabled Hybrid will add '-hwaccel auto' to ffmpeg decoding calls.

This option has no effect if the selected hwaccel is not available or not supported by the chosen decoder (only mpeg-2, H.264, VC-1 and WMV3 content are supported atm.).
Note that most acceleration methods are intended for playback and will not be faster than software decoding on modern CPUs. Additionally, ffmpeg will usually need to copy the decoded frames from the GPU memory into the system memory, resulting in further performance loss. So this option might not provide any additional speed and thus is mainly useful for testing.

Warning:
Only enable if your ffmpeg version and your Hardware does support DXVA2 (on Windows) or VDPAU/VDA (on Linux/Unix).

Assuming you are using ffmpeg for decoding (so neither Avisynth or Vapoursynth is used) this should work fine. (did here in a quick test)
If this does not work for you, please share a debug output of the job creation, thus I can see what settings were used and why QSV wasn't used.

If neither (Avisynth or Vapoursynth) are used and "QSVEnc->Hardware->Only use encoder" is enabled, QSV will be used for decoding, filtering and encoding.

If you use either Avisynth or Vapoursynth, whether QSV is tried for decoding depends on the used source filter and the selected option under "Vapoursynth->Misc- >Source" / "Avisynth->Misc->Source". To use QSV for encoding, you will have to use QSVEnc.


Cu Selur