5K iMac iTunes movies playback sometimes choppy

xWhiplash

macrumors 68000
Original poster
Oct 21, 2009
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Hey guys,

So I recently got my new 5K iMac 2017. Everything is fine except iTunes video playback seems to be choppy. Every couple of minutes there will be a period of 30 seconds of what appears to be low frame rate video playback. Audio is fine. I do not have this issue with my 2016 Macbook Pro or 2010 Mac Pro. If I connect a second display to my 2017 iMac, I do not have the issue either. Is there something I can do to make playback more smooth on the built in display? Is this a common issue, or is something else going on?

Thanks.
 

ZMacintosh

macrumors 65816
Nov 13, 2008
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are these iTunes purchases? If so are they HD and are they streaming from iCloud/iTunes or are they downloaded locally to the system?

Playing HD content on a recent 2017 5K iMac have not had any issues myself. Both on streaming from iTunes and Downloaded.
 

xWhiplash

macrumors 68000
Original poster
Oct 21, 2009
1,921
797
are these iTunes purchases? If so are they HD and are they streaming from iCloud/iTunes or are they downloaded locally to the system?

Playing HD content on a recent 2017 5K iMac have not had any issues myself. Both on streaming from iTunes and Downloaded.
Yes they are HD iTunes purchases. They are downloaded on my external SSD. I will download a movie on the internal SSD and check it.

Do you play the video full screen? I also experience lag switching between the full screen programs. For example, when I switch to my desktop from iTunes (at full screen), the side bar (recently added, movies, genres) stays on the screen until the animation is finished. I have the Radeon Pro 580 8192 MB. Is this normal behavior, or is there something wrong here?
 
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ZMacintosh

macrumors 65816
Nov 13, 2008
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I would be suspect of the cable or external drive. all of mine play off thee SSD built into the iMac with the higher end GPU. no lag between fullscreen or normal window size, its pretty fluid.
 

xWhiplash

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Original poster
Oct 21, 2009
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Actually I ran a couple of tests now. I copied the downloaded file from my external SSD to my internal SSD and it had the same issue. I re downloaded the movie to my internal SSD and it had very very minor slowdowns (only noticeable if you were really looking). Do I need to re download my stuff? Are you running High Sierra beta? I assume things will be smooth after it is on Metal in High Sierra. I always see lag when switching between full screen programs.
 

ZMacintosh

macrumors 65816
Nov 13, 2008
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no beta, 10.12.6 combo update, all downloaded locally to the iMac and some stream from iTunes.

Which films are these?


you could always try a partition on your drive with a clean OS and try them there and see if it resolves any.
 

xWhiplash

macrumors 68000
Original poster
Oct 21, 2009
1,921
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no beta, 10.12.6 combo update, all downloaded locally to the iMac and some stream from iTunes.

Which films are these?


you could always try a partition on your drive with a clean OS and try them there and see if it resolves any.
Deadpool and Star Trek (2009) were the worst ones. I just downloaded Passengers to my internal SSD and it did not have major issues. Using the same external SSD with my 2016 MacBook Pro does not produce these problems though.

Do you think it is a hardware issue? I don't mind dealing with it until High Sierra comes out, then things should be smoother since it will be running on Metal (the windowserver process).
 

ZMacintosh

macrumors 65816
Nov 13, 2008
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329
hm I have both of those bought through iTunes and watched a few 10-15 minute segments and did not notice stutter or lag.

I don't think it has anything to do with OS and may be a hardware issue (CPU, GPU, RAM, or even the video sync cable)

They have the Public Beta you can certainly try.
 

xWhiplash

macrumors 68000
Original poster
Oct 21, 2009
1,921
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hm I have both of those bought through iTunes and watched a few 10-15 minute segments and did not notice stutter or lag.

I don't think it has anything to do with OS and may be a hardware issue (CPU, GPU, RAM, or even the video sync cable)

They have the Public Beta you can certainly try.
How come it works fine if I put the video on my other display? Also, playing videos downloaded from websites in Quicktime have no lag. It just seems to be an iTunes thing.
 
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ZMacintosh

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Nov 13, 2008
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perhaps a reinstall of the os or a partition with a new macOS to test would be the next attempt
 

xWhiplash

macrumors 68000
Original poster
Oct 21, 2009
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perhaps a reinstall of the os or a partition with a new macOS to test would be the next attempt
I installed High Sierra on a new partition and the video playback is MUCH better. Could be the fact that it is a fresh install, or could be High Sierra's performance. Not exactly sure.

Edit: Got it working much better on my Sierra partition. I figured it out. So my extra monitor supports high refresh rate. When setting it to 120hz, iTunes on my iMac's display lags bad. When I set my extra monitor to just 60hz, iTunes plays much better.

By default, macOS just sets my monitors to 60hz for fresh installs, so it was working better on High Sierra because of that.
 
Last edited:

ZMacintosh

macrumors 65816
Nov 13, 2008
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There ya go, yeah if you have both the external monitor and the iMacs screen running that could be a huge reason for the lag. if you only do one or the other you should be fine
 

xWhiplash

macrumors 68000
Original poster
Oct 21, 2009
1,921
797
Thanks for the assistance! Now for some reason I cannot delete my High Sierra partition :(
 

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