Magnetic Mask analysis in FCP very slow on my Mac (M4)

I am new to FCP, but noticed that the analysis of a magnetic mask suddenly slowed from rather fast to very slow. I have been looking for answers on the internet and found a few...

1: which media type I am using

2: the viewer is set on entire render view disabled

And that is as far as I got with answers, but still my analysis is very slow.


iMac 24″, macOS 15.6

Posted on Nov 11, 2025 2:57 AM

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Posted on Nov 14, 2025 6:41 AM

Magnetic Mask should not "suddenly" become slow. However, it is sensitive to the clip duration. If you use it on a 60-second clip, then try it on a 15-minute clip, it may appear to suddenly become slow; however, analysis or export performance has always been dependent on the clip length, and it gets much slower on longer clips. In general, don't use it on a clip longer than 5 minutes. If you have a 30-minute instructional lecture and want to mask and adjust the speaker, blade the clip every 5 minutes and do those separately.


There may be possible interactions with other effects, but I don't remember those. I suggest you take a test clip, put that on a timeline with no other effects, use Magnetic Mask and check analysis and export performance. If that is also slow, give us the specifics. If it is fast, then incrementally add the effects used on your original timeline and see if it suddenly becomes slow with certain ones. State what those effects are.

7 replies
Question marked as Top-ranking reply

Nov 14, 2025 6:41 AM in response to Filos149

Magnetic Mask should not "suddenly" become slow. However, it is sensitive to the clip duration. If you use it on a 60-second clip, then try it on a 15-minute clip, it may appear to suddenly become slow; however, analysis or export performance has always been dependent on the clip length, and it gets much slower on longer clips. In general, don't use it on a clip longer than 5 minutes. If you have a 30-minute instructional lecture and want to mask and adjust the speaker, blade the clip every 5 minutes and do those separately.


There may be possible interactions with other effects, but I don't remember those. I suggest you take a test clip, put that on a timeline with no other effects, use Magnetic Mask and check analysis and export performance. If that is also slow, give us the specifics. If it is fast, then incrementally add the effects used on your original timeline and see if it suddenly becomes slow with certain ones. State what those effects are.

Magnetic Mask analysis in FCP very slow on my Mac (M4)

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