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Backwards shuttle sticky

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Oliver Peters
Backwards shuttle sticky
on May 8, 2018 at 7:49:25 pm

General question... Why is it that when I shuttle a video file fast in the "backwards" direction (J-key at 2X, 3X) it gets "sticky"? If I fast-shuttle forward (L-key at 2X, 3X) it's generally fine. This is across various apps and even with "optimized" media, like ProRes.

- Oliver

Oliver Peters - oliverpeters.com


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Bill Davis
Re: Backwards shuttle sticky
on May 8, 2018 at 7:56:48 pm

Maybe because frame caches are generally written to “read ahead” rather than “look behind” as their default?

But that’s pure speculation on my part.

Creator of XinTwo - http://www.xintwo.com
The shortest path to FCP X mastery.


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Oliver Peters
Re: Backwards shuttle sticky
on May 9, 2018 at 12:26:52 pm

Seems like a logical deduction. That would be my guess as well, but who knows?

- Oliver

Oliver Peters - oliverpeters.com


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Michael Gissing
Re: Backwards shuttle sticky
on May 9, 2018 at 11:07:49 pm

I see no reason why I frame codecs like ProRes would be any different going backwards. Mpeg or similar delta codecs sure.


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Bill Davis
Re: Backwards shuttle sticky
on May 9, 2018 at 11:27:01 pm

Still being admittedly ignorant, but I think Oliver is on. LAN or SAN.

My presumption is that unlike accessing a direct media pool, data caching is a big part of making performance smooth.

If the system is calling for and caching “frames ahead“ - but not “frames around” - that might necessitate a minor “catch u” needed when your skimming direction changes.

And it would be that way no matter the nature of the compression of encoding.

It would just be a tiny spate of network access overhead involved?

Again, just guessing.

Creator of XinTwo - http://www.xintwo.com
The shortest path to FCP X mastery.


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Michael Gissing
Re: Backwards shuttle sticky
on May 9, 2018 at 11:33:12 pm
Last Edited By Michael Gissing on May 10, 2018 at 12:38:06 am

A smart NLE should be caching frames ahead and behind so direction change is smooth. The size of the ahead buffer might be bigger than behind but as soon as direction changed, the buffers should adjust. With modern hard drives the direction change should be seamless. Any stickyness due to drives would manifest itself regardless of direction if the software controlling the caching was not optimal. That's why NLEs and DAWs have minimum RAM requirements.

If the buffers are optimised for SSDs or RAIDs then that is not smart software. Optimisation should be around the minimum spec.


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