The slowdown with RAM set to more than 10% is a long standing anomaly, also there in the 3.3.x release versions just at a generally lower speed level - but this is only the case with SD upscales.
When upscaling FHD to 4K you should set the RAM to 100% as this will be faster in that case.
Great to know, thank you!
And thanks for the video. Really strange, Iris does go fully havoc with that in the 3.4.0.1.a here as well:
And even more so if you chose Interlaced progressive:
And I can also reproduce that it does indeed work as it should on the 3.3.2 release version (which I still keep as this one somehow worked better than following 3.3.x versions.
I guess you should provide the source to the devs so that they can look into this.
I have sent the same file link that I sent to you privately to @suraj via the Dropbox link at the top of this thread as per your suggestion.
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I wondered a bit why my artifacts were so different to yours - and it seems this is a fully different issue.
Apparently the 3.4.0.1.a does not work under the current Beta os MacOS 14 “Sonoma” which I’ve just installed as I now get those artifacts as well with other videos that flawlessly worked before on 13.4 
Ah!!! Early beta macOS software can cause all kinds of funky things so I’m not totally surprised! Having written that, I’m on Ventura 13.5 & it shows the groovy lines as per per original post ^^^ 
Strange also that you had 13.5. Here 13.4 was the latest version that was available for me; no update could be found - besides the Sonoma Betas, of course.
So maybe those lines were already a 13.5 vs. 13.4 thing…
13.5 was released on July 24th but yeah you could be right about 13.4 vs 13.5. I have no way of checking though!
20 FPS? Dang, I’d commit a crime for that. I Get 2 FPS on my 5 year old intel iMac. It’s better than the .9 FPS I was getting previously.
I have seen one other report of this as well. If you are able to provide reproduction steps that would be superb! It seems intermittent which will make this difficult to pinpoint.
Do you see this with the preview and the export or one or the other?
I see that you shared the file with Suraj, thank you!
