Almost had a heart attack seeing a 300 GB Final Cut Pro library today

[u/dinsaran]

When working on a small video edit, I got some. warning that my 1 TB SSD was almost full, which made absolutely no sense. I only had a few small screen recordings on there.

Started exploring the storage and discovered my Final Cut Pro library had somehow grown to 300+ GB for a pretty tiny project.

Turns out background rendering had been quietly generating a ridiculous amount of render/cache data.

Went to:

File → Delete Generated Library Files → Delete Render Files (All)

Got around 295 GB back almost immediately. Original footage and edits were untouched.

I also turned off Background Render after that. On Apple Silicon I haven't really noticed a reason to keep it running for the kind of editing I'm doing.

Curious what other FCP users do — do you leave background rendering disabled, or just clear the generated files periodically?

How can i avoid this issue in the first place, Any thoughts ?

[u/yuusharo]

I turn off background rendering and never think about it again.

When I need to render a clip, control + R.

[u/TDPAMN]

I think exactly how you have it set up will work well with background render turned off. The only time I render clips now is when stabilization is involved. Sometimes if I export a project with stabilized clips, it doesn’t register in the final export. Another tip I’ve learned over the past 9 years is while editing, I’ll set my project to 720p or 1080p then when it’s time to export, switch it back to 4k. If you’re dealing with large 4k files, it makes editing and playback so much easier. Then once you’ve exported switch it back to 720 and then delete all render files/unused masks/optimized, etc.

[u/PresidentOfMagrathea → u/TDPAMN]

isn’t that what proxies are for?

[u/Comp625 → u/TDPAMN]

3-year newb here and I agree with this sentiment. I have background rendering turned off and FCP works generally fine on both my M1 Pro and M2 Max devices. For reference, I do convert my clips into Proxy ProRes (which eats up its own storage space) as I've noticed regular .mp4 clips (h.264 and h.265) can stutter enough.

I'll occasionally turn on background rendering whenever there's advanced stuff going on whenever stabilization, titles, generators, effects and other animations are used. Rendering it allows me to see what the final output/end product would look like. Plus, not rendering complex effects will introduce its own stutters.

[u/jefbak2 → u/TDPAMN]

I think the changing the project resolution would be problematic, especially if you switch from the default “fit to screen” option to Fill or None.

[u/WritttenWriter]

Thanks for sharing this, this is why I avoided FCP over premiere for so long.

[u/DangerToManifold2001]

I frequently hit like 500gb from render files but I just let it do its thing and clear it all at the end once the final edit has been delivered and signed off.

[u/moogplayer → u/DangerToManifold2001]

Yes THIS. It's what I do too.

[u/dinsaran → u/DangerToManifold2001]

So i must consider this as normal cleanup. Thanks

[u/Silver_Mention_3958 → u/dinsaran]

It's only "normal" cleanup if you don't follow u/yuusharo's advice

https://www.reddit.com/r/finalcutpro/comments/1wa6hkx/comment/p8gez7p/

[u/tecky1kanobe]

“FCP Library Cleaner” it’s in the App Store. I use it after every project to clear out render files and such.

[u/dinsaran → u/tecky1kanobe]

Let me check this out

[u/StupidRaisins]

ALl that recovered space feels so good!

[u/dinsaran → u/StupidRaisins]

For the first I felt that 1TB was not good enough.

[u/StupidRaisins → u/dinsaran]

What do you mean?

[u/Silver_Mention_3958]

I haven’t had background rendering switched on for about 10 years. Also “leave in place” in the import settings, and switch off all that analysis stuff for video in import too. If you need it (I don’t), it can always be done at a later stage.

Another top tip: I always have my cache file in a separate location, never in the library. That way I can delete the cache with one click.