Apple ProRes 444 can not be transcoded in FCP?

@ontop, I received your project XML file. The problem isn't the ProRes 444 clip. Rather, below that clip are four other clips, some of which are nested compound clips, each containing several effects. There are about 25 effects in the nested clip stack over the range of that ProRes 444 clip (see below).

The FCP render cache is not generated per clip. It is generated on a span or range of the timeline for all clips in the stack covered by that range, including all nested compound clips. If any part of any effect on any clip in the nested stack is changed, the entire thing (including all 25 effects) must be re-rendered.

Ideally it could be rendered just once and persist through re-launching FCP, assuming you didn't edit or alter any effect on any clip in that entire nested stack. However, all built-in FCP effects are implemented by the Motion runtime engine.

There are cases where complex interactions between multiple effects prevent that timeline range from being cached. There are various manifestations of this, including render dots remaining present after rendering to cache or render dots disappearing, but functionally, caching does not happen.

I have discussed this with FCP development, and my understanding is the current overall caching behavior is working as designed, but if specific, reproducible, well-documented scenarios are filed, they may examine it.

For your situation, the problem isn't caused by that ProRes 444 clip; it's the 25 effects in a "Russian Doll" series of nested clips and effects below that ProRes clip. I suggest you examine those and re-think what you actually need, considering the vintage and configuration of your machine. I'm actually not sure my top-spec M1 Ultra Mac Studio could run that smoothly.

I number the outer-layer clips from top to bottom starting with 1:

1: Top clip: "Bird Flying"
	- Green Screen Keyer
2. "NextRemembrance Clip 1" (Compound Clip):
	- Color Board
	Inside above CC:
		- Another CC "Remembrance Clip"
		- Sharpen
		- Color Board
		- Vignette
		- Streaks
		- Aged Film
		- Distort
   
			Inside above CC:
				- Image clip IMG_7121
				- Color Board
				- Image clip IMG_7107
				- Vignette
				- Color Board
				- Fisheye
				- Audio clip
				- Exciter
3. Generator clip
		- Opacity
		- Transform
		- Distort
4. Remembrance Clip (Compound Clip)
		- Color Board
		- Vignette
		- Aged Film
		- Gaussian Blur
		- Bokeh Random
			Inside above CC:
				- Image clip IMG_7121
				- Color Board
				- Image clip IMG_7107
				- Vignette
				- Color Board
				- Fisheye
5. Audio Clip
		- Exciter

FCP will not transcode if the media is already in an codec that is "optimal" for editing, like any form of ProRes, or the old DV codec.

You can transcode in Finder: control-click, select Encode Selected Video Files, and choose ProRes, but I have to ask: why? You can perfectly well edit with the footage in ProRes 4444. Besides, and I don't know if it's the case, 4444 supports alpha channel, so if there is some transparency in those clips, it will be lost when transcoding to 422.

ProRes 4444 by itself should normally not require rendering. But if you put effects on that, it will require rendering. Once rendered to cache, that generally should persist through re-launching FCP. However, there are some cases involving certain effects where that doesn't happen.

There is a separate issue about how your stock footage ProRes 444 or 4444 file was generated. If it was generated by FFmpeg, that is not a licensed ProRes application, and the behavior can be unpredictable. There have been previous problems with alpha channel behavior where the ProRes 4444 file was generated by certain versions of FFMpeg.

You can examine your ProRes 444 file with the third-party utility MediaInfo. If it says something like "Writing application : Lavf61.7.100," that was produced by FFMpeg.

@ontop, please export a project XML, compress that and upload to this location. I will examine your project characteristics and see if there is any known issue with the effects on that clip, which might account for the observed render cache behavior. https://we.tl/r-GbysenYWSi

To do this, just select the project icon in the left sidebar of the Event Browser, then do File>Export XML.

We also need to know what version of MacOS and what version of FCP you are running.

Rendering is not related to optimization. Rendering creates cache files for a project determined by the project properties. If the media doesn’t match the project rendering will occur, unless it’s switched off in preferences. I think the great majority of users always switch rendering off and leave it off.

That's a pretty old machine, too. Not the most powerful. And ProRes4444 does take some horsepower due to the very high bit rate.

I haven't received it yet. Please try again.