8K ProRes Raw footage becoming overly soft when edited/exported on 4K timeline in FCP.

Nothing says it has to be extra sharp! Anytime you convert image size, you'll have some degree of image quality loss, period. A native 4K image is sharper than a resized 8K image, as it is using all original, unaltered data. The shrunk image has lost data in order to fit into the smaller size, the pixels have to be rearranged. FCPX is not the best at resizing video footage.

You could get something like Topaz AI Video and that'll do a fantastic job resizing it, but you have to pay for it, and it is slow at processing, but gives about the best resizing results on the planet.

PLUS you're going to H.264, which although it has come a long way and can produce some stunning image quality, I'd try exporting your stuff as ProRes 422 and see.

I don't have any 8k ProRes RAW but I have lots of 6k ProRes RAW from our DJI Ronin 4D and also 8k RED RAW from our V-Raptor.

I tried the 6k ProRes RAW in a 6k and 4k timeline, exported as 6k and 4k from the 6k TL using H.264 and ProRes 422, also the 8K R3D in a 8k TL and 4k TL, exported as 8k and 4k PR422 and H.264 from the 8k TL and 4k from 4k TL.

I viewed it on a calibrated 5k Apple Studio monitor. I couldn't see much difference in any of the permutations.

If you are viewing 8k on a 5k or 6k XDR monitor vs 4k on those same monitors, in theory the 4k should be less sharp -- it has 1/4 of the pixels of the 8k frame. If you are viewing it on an HD monitor, iPad, etc. I'm not sure you could see the difference.

If the final product will be uploaded and re-encoded for streaming, I tend to doubt you could see a difference during playback.

However I remember years ago there were some issues with FCP whereby 4k downscaled to 1080p seemed to be a bit too soft. I don't remember if that was resolved or defined as expected behavior.

As Ben said, anytime you rescale there will be scaling losses. That is why in Photoshop there are various resampling and scaling options (see attached). There is no single best way to rescale an image -- each algorithm has various tradeoffs.

I vaguely recollect some NLEs automatically add sharpening when rescaling, and FCP does not.

I suggest in FCP, duplicate the timeline, then in that timeline, remove all the effects with Edit>Remove Effects. Pick a frame and put a marker on it. Use the R key to draw about 2 frames, then export that as 4k H.264. Then do that in an 8k timeline with the ProRes RAW material, mark the same frame with the M key, use R to draw about 2 frames on the timeline and export that as 8k H.264. Examine those in Quick Look or Quicktime Player and see if there is any visible difference.

A lot of people noticed this behavior when using a "multiscreen" effect I created awhile back. If the pixel size of a clip does not exactly match the project size, and (certain kinds of) Effects are added, clips can soften when scaled down — which is really strange! — to say the least.

Try making your clips a compound clip before exporting. If that doesn't work, then copy the effects from your clips, turn them off in the inspector, then Paste Attributes to the compound clip. This will necessitate making every individual clip a compound clip if you have different effects and effects parameter settings for each individual clip.

HTH - no guarantees!

Could you give the complete specs of the original media from MediaInfo or Invisor?

Although the title concerns soft footage, there are two separate issues mentioned. (1) The soft footage and (2) The various color conversion pathways from ProRes RAW to the final distribution codec.

The color conversion issue is quite complex, esp. when dealing with ProRes RAW, so I'll respond to that tomorrow.

I don't fool with 8K footage (yet) but I weekly use 4K content in a 1080 Timeline, and have no quality issues at all. But I do notice my focus has to be EXACT or that 4K gets fuzzy fast.