HD video on iMac

Discussion in 'iMac' started by leverbo, Jan 5, 2014.

  1. leverbo macrumors newbie

    Jan 5, 2014

    I am a Windows user who is seriously considering switching to Macs. I visited my local Apple Store and I found some curious things happening when playing HD video and I hope someone can shed some light on this because I can't find anything about this online.

    Apparently, every computer in the store has a short trailer of "Oz, the great and the powerful" on its disk.I tried to play it full screen on two machines:
    1) a 27" i5 iMac
    2) an i7 Mac Mini connected to an Apple thunderbolt display

    The iMac was performing very poorly. The video was constantly stuttering quite noticeably and I believe anybody would say it was not smooth.
    The Mac Mini wasn't perfect, but it was a lot better ans perhaps some may not notice the stutter.

    Just to rule some things out, I downloaded VLC on the iMac and there was no change compared to QuickTime.
    I must say I am a bit surprised because I thought in 2014 any modern computer would be capable of handling HD content without particular problems. However, I am even more surprised by the lack of information on the internet on this subject. The 27" iMac has the most gorgeous screen I ever laid my eyes on and I am sure millions of people must have bought it and watched HD movies on it. How is it possible that no one is complaining on the web? Does anyone have any experience to share on this subject?

  2. leverbo thread starter macrumors newbie

    Jan 5, 2014
    I will add something to view it from a different angle.
    Does the thing I saw depend on the CPU, the graphics chip, the output interface or what?
    I couldn't find in the shop any i7 iMacs. Can I assume that the HD video behaviour on those would be more in line with an i7 Mac Mini? I'd like to understand where the bottleneck is.
  3. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    Most likely it depends on the GPU.

    Systems with integrated graphics (Mac Mini, low-end 21.5" iMac) may perform poorly in this.

    My early-2011 MBP stuttered badly on Intel HD 3000, and it played silky smooth after I forced the GPU into the Radeon card (with GFXcardstatus).
  4. leverbo thread starter macrumors newbie

    Jan 5, 2014
    I see your point, but the iMac equipped with the so called "NVIDIA GeForce GT 755M with 1GB " was struggling more than the Mac Mini.
  5. yjchua95 macrumors 604

    Apr 23, 2011
    GVA, KUL, MEL (current), ZQN
    Is the video playing through QuickTime or Safari?
  6. leverbo thread starter macrumors newbie

    Jan 5, 2014
    I tried QuickTime and VLC and the results were the same.
    Some time ago I also tried to watch a full HD video on youtube, which I believe to be flash with similar results. It doesn't seem to depend on the video or the technology used to play it.
  7. DavidBlack macrumors 6502a


    Jan 27, 2013
    Somewhere In Apple's HQ ;)
    I have an iMac 21.5 2012 without the fusion drive and I can tell you from experience some videos lag because of hard drive. I did a test I played a 1080p video in QuickTime Player then as the video was playing I used disk speed test to test the performance of hard drive and the read and write speeds dropped considerably. I am guessing because it's reading the data while it's playing the video. I did notice however in OS X Mavericks the problem went away. Maybe it's a combination of hardware and software with the software not being optimized property, but I maybe wrong.
  8. joema2 macrumors 68000


    Sep 3, 2013
    I play HD video regularly on two different iMacs:

    - 2012 i7 @ 3.4Ghz with 16GB RAM, 3TB Fusion Drive, GPU = 675MX 1GB
    - 2013 i7 @ 3.5Ghz with 32GB RAM, 3TB Fusion Drive, GPU = 780M 4GB

    I edit HD video regularly using FCP X on a 2011 iMac i5 @ 3.1Ghz with 16GB RAM, GPU = AMD 6970M 1GB. It works fine. HDD = 1TB 7200 rpm internal drive, video files on 3TB external 7200 rpm Firewire drive.

    I downloaded and tested the below HD 1080p video on both iMacs using VLC 2.0.8, VLC 2.1.1, VLC 2.1.2, and Quicktime Player. All combinations on both iMacs played perfectly with no lost frames, and scrubbing forward/backward was fluid and fast.

    For H.264/MPEG-4-encoded video (many downloads and Blu-Ray), it's rare for hard drive speed to impact this. The disk transfer rate for 1080p is about 3.5 megabytes/sec, well within the range of the slowest hard drive. For MPEG2 HD video, the data rate is about 2x that since compression is less, but it's still within the range of most older hard drives.

    This video was shot in 4K and down-sized to 2k (1080p). You can download the 474MB 1080p file for testing. This is simply the first file I saw when looking for a test video.

  9. leverbo thread starter macrumors newbie

    Jan 5, 2014
    Thanks everybody for the replies. The video I saw at the apple store is actually from Apple and I downloaded it here:

    I downloaded the video joema2 was suggesting and its bitrate is way higher!
    I'll put this video on a USB stick and visit the Apple Store and see what happens.

    However, it would be very stupid from Apple to pre-load content that can't be played flawlessly on their demo machines. I did not go to the Apple Store trying to cripple their hardware, I was actually trying to see how hot (or cool) a Mac Mini runs while performing an intensive task and playing HD video was the first thing that came to my mind there and then. If it wasn't for the poor quality of the video, I would have probably bought a mac by now.
  10. joema2 macrumors 68000


    Sep 3, 2013
    Be advised it's not possible to easily download that, at least using Safari on Mavericks. Apple has apparently disabled direct download from their trailer site.

    You can download it by jumping through various hoops:


    Or just going to here:

    If you downloaded the video from Apple using a "download helper" tool in Chrome or some other browser, it may have re-encoded the file in a format which makes playback sluggish.
  11. leverbo thread starter macrumors newbie

    Jan 5, 2014
    Being someone who wants to migrate to Apple, I am still a Windows user and I don't know if that's the reason but I could download the file. I did it with Chrome, though, so I don't know if a plug in was involved.
    Anyway, the one I tried at the Apple Store was in iTunes and I think was downloaded properly.
    Anyway, my 2009 Samsung TV via an USB stick cannot play .mov files. So I re-encoded it quickly to mp4 with a rubbish Windows Movie Maker program. I don't know if this killed it, but the higher big rate movie you recommended plays FLAWLESSLY on my old TV while this one struggles. I am really wondering if it's something about the file itself. I'll take the other one to the Apple Store and verify. At least this would explain why no one is complaining about lack of HD performance. However, it would be very silly of Apple to put their potential customers off this way...
  12. Twimfy macrumors 6502a


    Sep 11, 2011
    Well I downloaded the exact same trailer in 1080p and it runs flawlessly in fullscreen on my 2008 iMac which is a C2D. In fact just for good measure I had it playing in VLC, Quicktime and Safari all at the same time...never missed a beat.

    There's clearly something odd going on here with the video they're using as I know that even the 2007 Macbook's can run 1080p video without too much trouble so I wouldn't let it put you off buying an iMac. Remember they're used industry wide on many of the TV's and Movies you watch on a regular basis.
  13. joema2 macrumors 68000


    Sep 3, 2013
    Very likely Windows Movie Maker messed up the file. It probably had default transcode settings which degraded it. This is very common when converting between video formats, and not just by Windows Movie Maker.

    Handbrake is a powerful and free video converter. You could try that: http://handbrake.fr

    The bottom line is the lagging video is apparently caused by the conversion process, not by inadequate playback capability of the iMac.

    I have both Windows and Mac computers for video editing. You can get the job done with either one, although Windows 8 is pushing me toward the Mac side :)

    If you get a Mac you might consider also purchasing the optional One to One training. It's a pretty good deal: http://www.apple.com/retail/learn/one-to-one/
  14. leverbo thread starter macrumors newbie

    Jan 5, 2014
    Hi everybody. The surprises continue. I visited again the Apple Store and I tried the same two computers: the i7 Mac Mini and the i5 27-inch iMac. This time, I brought a USB stick with me containing the HD video Joema2 suggested.
    As I said, I had tried already the USB stick inserted into my 2009 Samsung TV, where it played flawlessly.
    Now. Both computers, playing from the USB stick experienced stutters, meaning that the video would stop playing for a very noticeable fraction of a second and then restart. This would happen occasionally. This alone was making the experience worse than on my TV, but in the real world I would not be playing from a USB stick, so I copied the file onto the hard-drive and re-tested. That particular issue went away. The overall video playback was acceptable, meaning that watching and enjoying a movie would not be a problem. HOWEVER, the playback was far from the smoothness I experience on my TV. For instance, it is quite noticeable on a moving shot of the moon 22 seconds into the video. Considering that TVs are mostly used to display content played elsewhere (blue-ray players, consoles, etc.) and, especially 5 years ago, playing from USB sticks or DLNA was quite a niche market for them, I'd be really surprised if the modern CPUs and graphics chips on a computer were less powerful. This must be a software issue. As I said, it is not something major and it's barely noticeable. However, right now I do not own a computer capable of outputting 1080p content to a TV, so the way I watch 1080p content is copying it to a USB stick and plugging it into the TV. It would be rather disappointing to spend a considerable amount of money to get a modern popular computer, connect it to the TV and see the quality get worse.
    Said this, there are still 2 things that I have not tested:
    1) I am comparing a 1080p native TV with higher resolution monitors, so I can't say whether the upscaling could be the issue
    2) I have not tested this particular video on a 1080p screen using a Windows PC. This I may be able to do on Monday.
  15. joema2 macrumors 68000


    Sep 3, 2013
    Note sure why that happened, but as you found, copying to the hard drive is usually best. There is an extremely wide range of performance in USB thumb drives. I have tested older USB 2.0 sticks at 5 megabyte/sec, and a new Lexar Triton USB 3.0 stick at 174 megabyte/sec. Even 5 MB/sec should be adequate for HD playback, so cause of the stuttering is unclear.

    That is a time lapse shot on a 24 frame/sec video. Any video, (but esp. 24 fps) is susceptible to "frame judder". This happens whenever an object moves across the screen above a certain rate, or the camera rapidly pans. Even though it's a time lapse shot, the same situation applies -- that video file (like most cinema film) only has 24 frames/sec in it, so this imposes a limit on how rapidly objects can move through the scene without judder.

    The only exception is using motion interpolation (sometimes called "optical flow" or frame rate interpolation) which essentially fabricates in-between frames based on a best guess. A software example of this is Twixtor: http://www.revisionfx.com/products/twixtor/

    Lots of newer TVs have motion interpolation in hardware. It can typically be turned on/off, and sometimes adjusted. This is because it can creates undesirable artifacts. Some video player software can do real time motion interpolation during playback, but I don't think VLC or Quicktime Player can: http://en.wikipedia.org/wiki/Motion_interpolation

    It's possible your TV had motion interpolation turned on. Check your owner's manual and the menus. I think this would also process the video from an iMac used as a playback source (via HDMI). So it's conceivable certain video material might look look better on your TV than iMac, even if the iMac was the player in both cases.

    No guarantees, but it's possible connecting an iMac or MacBook to your TV via HDMI would also look better. I sometimes connect my 2013 MacBook Air to my 62" Samsung DLP TV via Thunderbolt->HDMI, and it looks good.

    Modern computers definitely have sufficient CPU and GPU power for real time motion interpolation. The problem is not all player software implements this.

    I played it on my 2013 iMac, my 4Ghz i7-875K Windows 7 PC, and my 13" 2013 MacBook Air with i7. It looked good on all of them. I can see a slight amount of frame judder on the moon scene at 0:20, but only if I look for it.

    On my PC I tried VLC and PowerDVD ver. 11 (which has motion interpolation enabled). I couldn't really see a difference -- in both cases the frame judder was minor. The iMac looked the same in both Quicktime and VLC 2.1.2.
  16. CH12671 macrumors 6502

    Dec 29, 2013
    Southern US
    Just played the apple trailer on my mid 2012 13" MBP i5 and it was flawless....
  17. leverbo thread starter macrumors newbie

    Jan 5, 2014
    I was aware of motion interpolation. On my TV it goes under the name of "100 Hertz". I've got it disabled.

    It is possible, however, that some additional "smoothness enhancement algorithms" are not configurable and this is the only explanation I can find... I am really curious to see what happens on a Windows PC. My old laptop judders a lot more than the iMac did. At work, I have two colleagues with brand new machines: a Lenovo laptop and a MacBook. I'll try to setup a side-by-side comparison on Monday and post the results.

    And yes, the discussion is academic. Indeed, I am talking about something you only see if you look for it.

Share This Page