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27" iMac struggling to edit 4K iPhone footage

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alex ezorsky
27" iMac struggling to edit 4K iPhone footage
on Oct 14, 2016 at 9:36:33 pm

Ever since the iPhone offered 4K shooting at the same time that 4K cameras still started around $3,000 the video world stopped making sense to me.

Now things make even less sense considering I get lightning fast scrubbing playback of my 4k videos on the iPhone itself.

But when I play back even a relatively simple sequence using this same footage imported into Premiere 2015 it plays fine for about 20 seconds but then upon any transitions, edits, or time stretched clips starts choking, lagging and is soon painfully lagged and frustrating.

I know 4K is generally a proxy workflow but these 3840 x 2160 files have bitrates around 60mbps.

My specs:

iMac (27-inch, Mid 2011)
3.4 GHz Intel Core i7
20 GB 1333 MHz DDR3
AMD Radeon HD 6970M 1024 MB

And I've tried editing off of my SSD core drive, my internal 7200rpm drive and my QNAP raid 0 NAS

- I've tried editing in a 4k sequence and lowering playback to 1/8.
- I've tried downscaling it all in a 1080 sequence
- I've tried clearing my cache
- I've tried changing the ram allocation
- I've tried changing the playback engine to Open CL and back
- I've even re-installed the OS

Am I going crazy or can someone out there confirm that my machine should be more powerful than my iPhone and handle editing this footage fine.


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Dave LaRonde
Re: 27" iMac struggling to edit 4K iPhone footage
on Oct 14, 2016 at 9:41:38 pm
Last Edited By Dave LaRonde on Oct 14, 2016 at 9:44:20 pm

That's because Apple CHEATS.

You work under the delusion that iPhone video is every bit as good as video from a real camera. Well, it isn't. The biggest problem is that iPhones shoot at a variable frame rate. I guess it saves on storage. PP expects a CONSTANT frame rate.

You need to transcode your footage to a media container & codec that plays nicely with PP. I like quicktime movies in ProRes 422 (I assume you have that), Photo JPEG, JPEG 2000 or PNG codecs.

Let's hope the speed variations that occur by going to a constant aren't too noticeable.

There are also iPhone apps that will make the thing shoot at a constant frame rate. Get your mitts on one of them... and keep close tabs on your storage.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA

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Alan Lloyd
Re: 27" iMac struggling to edit 4K iPhone footage
on Oct 14, 2016 at 10:49:43 pm

Until quite recently, Wirecast used to only offer variable frame rate as well.

My hair is somewhat grayer due to having to try to edit a webcast archive done that way.

Thankfully, there were PPT slides to put over it to cover the pull-ups needed to (temporarily) regain audio sync.

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Al Bergstein
Re: 27" iMac struggling to edit 4K iPhone footage
on Oct 15, 2016 at 9:08:21 pm

Yes, variable frame rates are a nightmare. So I agree with the recommendations. However, I think that for 4K you also are going to struggle with a 1GB video card. That worked great for SD and even some 720p footage. But you are likely to find yourself having problems keeping up with 4k footage with that.


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Ann Bens
Re: 27" iMac struggling to edit 4K iPhone footage
on Oct 16, 2016 at 5:14:09 am

Convert to constant framerate with Handbrake before bringing it into Premiere.

Adobe Certified Expert Premiere Pro CS6/CC
Adobe Community Professional

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