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Why does Logic Pro use VTDecoderXPCService?


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Short version: see subject.

Long version: occasionally Logic gets in a state, when idling, where the CPU core normally used for live input is using 100% of the available cycles, rendering the program useless for tracking. (That is from Logic's own CPU meter.) Looking at CPU usage with Activity Monitor shows VTDecoderXPCService right below Logic Pro for CPU usage - about 17%.

Quit and restart Logic right away and the problem persists, with VTDecoderXPCService sucking up 17% of available cycles even with Logic not running. Restart Logic and its live input core spins madly, useless.

Now the interesting part. Quit Logic and wait for about a minute, until VTDecoderXPCService drops off the list of high CPU usage in Activity Monitor. It's still a running process, but it's not spinning. Now launch Logic. Voila, problem fixed, Logic runs fine, CPU core 0 is barely running.

It sure seems to me that a) VTDecoderXPCService sometimes gets in a spinning state, and  b) when that happens, Logic is crippled. There is  1-to-1 correspondence between VTDecoderXPCService spinning and Logic being unusable.

Now...huh? VTDecoderXPCService is for video decoding. I don't have any video running anywhere when this happens, in Logic or anywhere else (browsers, QuickTime, etc.). Why would Logic be affected in any way by what VTDecoderXPCService is doing? 


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It's a macOS video and audio API, used by apps to convert video and audio, so it's not surprising that Logic might use it for various tasks. it's used for a lot of things, including rendering content in Messages, video playback in web browsers and so on.

However, it could be something on your system that is hanging the process, and thus Logic isn't getting a response from it, rather than a Logic problem per se.

When did this behaviour start on your system?

There's a lot on google about this process taking up CPU on Macs generally.

Edited by des99
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3 minutes ago, des99 said:

When did this behaviour start on your system?

I'd say sometime in the last 3 or 4 months. Unfortunately, many major components have been updated in that time - Logic, macOS, many of the plugins I rely on. 

Do you know what VTDecoderXPCService is used for in the context of audio? Logic shouldn't really be doing any "decoding" as far as I can see, it doesn't use or create any encoded audio other than when importing audio, and possibly during a bounce. Neither of which I am doing.

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I don't know what what services that component provides, or how things like Logic, FCP, and macOS generally uses it (other than a bunch of things I've already seen people say it does, from a quick search.

If you google the name, you will see a lot of reports of this process behaving poorly, so my guess it's it's something that's occurring on your system, that also consequently affects your Logic use, rather than something that Logic is specifically doing (or not doing).

Try googling around in the context of that service and seeing what fixes and mitigations people are doing to solve that problem when they have it, would be my best advice.

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