Quicktime 1080p video stutters at double size (on a very beefy system, too)

Discussion in 'Mac Pro' started by Oreckel, Sep 18, 2006.

  1. Oreckel macrumors newbie

    Sep 18, 2006
    Hi all,

    I'm trying to build a video wall, and right now I'm considering the option of using a Mac Pro to power four LCD monitors with a quicktime video being played at full screen. Right now I have a Mac pro and three LCD monitors, which I've arranged on my desktop in a grid pattern, giving a resolution of 3840x2104. I've rendered a quicktime movie of a white box bouncing around the screen at 1920x1080 resolution (compressed with H.264, the file size is hardly 2MB - incredible!). When I play the file at full screen on just one of the monitors, it plays like a dream, just beautifully. But, when I go to View > Double size so that it fills all four screens, the video just lags out the whazoo. I estimate it runs at 2-4 frames per second. This is sad, because I can't quite figure out where the hiccup is.
    • It's not the decompression - it's a 2MB file so it's not juggling billions of bytes (the fact that it plays fine at 1920x1080 prooves that it isn't the decompression)
    • I don't anticipate that it's the specs in the computer. I should find out for sure by opening four copies of this video and playing it individually on four screens at once, but so you know what I have:
      • Dual-core CPU I believe (I'm not positive, though)
      • 4GB Ram
      • 2x GeForce 7300GT (256MB ram; 10.7GB/s bandwidth; fill rate of 2.8 Billion pixels/sec each)
      • Roughly 480GB free disk space

    It just seems to me like this computer shouldn't have a hard time playing this video. My theory is only that Quicktime isn't effectively using the hardware in the system (as in, no hardware acceleartion) and that it's relying on the CPU to render everything. That's a fair possibility, but I don't see why it is doing that. The hardware is there, and I'd like it if quicktime could use it. Does anyone know if there's a way to enable hardware acceleration for Quicktime videos that I've missed and may have gotten disabled by default? I looked around but saw nothing on the subject.

    Thanks a lot :).
  2. zflauaus macrumors 65816

    Nov 19, 2004
    First of all, wow. Four monitors. That's just, ugh... I envy you...

    Okay, what I can think of is that even though it is a 2MB file, the Mac Pro has to decode that file to actually read more than 2MB. If you compress a video file, none the less 1080p hi-def, to 2MB, your computer will have that much more to decode to make video appear. That is what I am assuming is happening.

    Also spanning out over multiple screens can sometimes make things lag. And if you have a Mac Pro, it is a dual-core processor. It could also be that the 7300GT just isn't up for playing 1080p. I know I'm going to get bashed for saying that.

    Good luck.
  3. balamw Moderator


    Staff Member

    Aug 16, 2005
    New England
    You're serious aren't you?!?

    IMHO The problem is the scaling. You're asking the display to handle updates of 1920x1080 (x2x2) (x24) (x30) = (resolution)x (scale factors) x (color depth) x (frame rate) = 5.5 Gbps!?! I'm amazed it works at all.

    BY the time you are scaling the video by 2x you're handling all that uncompressed data and you don't get a beneift from the compression as you do unscaled.

  4. baxterbrittle macrumors regular

    Nov 8, 2005
    Just quickly - does the video need to be distrobuted? If not run it uncompressed. Just a thought anyway. Also you might be better off getting a DVI videowall box that makes all the screens become one screen. That way OS X sees all your screen as one large screen. The advantage of this is that y one video card is displaying the video and there will be no syncing issues (I'm not actually sure there are syncing issues but considering your problem I wouldn't rule it out). Also you will be able to run full screen rather than windowed. As far as I know quicktime handles the scaling differently when blowing up a window to playing full screen. I guess I'm just rambling but it is worth looking into.
  5. Oreckel thread starter macrumors newbie

    Sep 18, 2006
    Thanks all to your replies thus far :).

    That was my theory, as well, but the video plays just fine when it's at 100% size, so I really don't think it's a problem decoding the file. The fact that only when I stretch the file it stutters implies to me it's a matter of display hardware, not the decompression (since it's not doing any more decompression at a larger size than a smaller size).

    I don't see where your units came from, but I'll agree - it's a huge amount of data to process (even though I theoretically have 2x 10.7GB/s bandwidth available). Do you think it would work better if I actually have the video rendered at 3280x2104? That way it won't have to scale it.

    The only distribution that needs to happen is over a LAN, so no - I'm not worried about the file's size. I thought about running it uncompressed, but the original, uncompressed avi that came out of After Effects clocked in a over 2GB for this 4 second file, and that stuttered a lot when I played it. I think it's fair to say that's because it just can't decode and process 500MB every second (but perhaps I'm wrong there).

    I'm thinking that perhaps, I may just want to run each monitor at half the resolution. I really can't anticipate people putting their eyes right up against the screen, and so maybe it's enough to run each display at 1024x768 (or whatever the 16:9 equivalent is). I'll experiment with that, as well (though I'd like to get this working, since it just seems a dedicated $4,000 computer should be able to pull this off).

    But I still believe, theoretically, it should work. Does anyone know, when I play the movie full screen on one monitor, if both video cards are being used to process it? I would think not. Since it's only on one screen, wouldn't it really only use part of one video card, because it's only being outputted onto the one screen?

    Now, assuming that's true, shouldn't there be no reason why it wouldn't work at 4 times the pixels, if it can then use four times the power (the aditional video card)?

    My theory is destroyed if it's fact that it's using both video cards to render the movie when I play it on the one screen. But I have a feeling that's not the case (each video card should really be working independently), and that what's happening here is that it's still trying to use only the one video card despite the fact that it's spanning multiple monitors (due to a flaw in how Quicktime decides to process the data). I think it may also be that the video cards are simply not being used at all, and if that's the case, I can see why just the processor would stutter at such a large resolution.

    Are there any other OS X media players I can try to see if they'll work better with hardware acceleration? Also, can anyone confirm or deny my theory that Quicktime isn't using some/any of my video cards, and if so, what to do to fix that?

    Thanks again :).
  6. Mackeyser macrumors member

    Jul 22, 2002
    Tampa, FL
    Remember, on a Mac Pro, one video slot will be set at 16x, the others will be at 8x, 1x and 1x.

    It could be that the two 1x slots are gumming up the works. You may find that reconfiguring your PCIe slots to 8x, 4x, 4x, 4x will work better as that falls under the limit of 26x (which is crazy as it SHOULD be 32x).

    Also, are all the cards 7300GTs? I wasn't clear on that from your initital post. That likely is me, but what exactly is your setup?

    Lastly, getting a DVI wall versus expecting the Mac Pro to drive all those monitors may be the best alternative and allow you to run it all at max res.

    But I'd check the PCI configuration
  7. Oreckel thread starter macrumors newbie

    Sep 18, 2006
    What exactly do you mean by that? The physical position of the graphics cards in the computer affect the attention they get? If you can elaborate a bit more I'd appreciate it - I don't quite see what you mean.

    Yep - both cards are 7300GT's. My configuration is still in my first post - if you want more details than that let me know.

    What do you mean by getting a DVI wall "instead"? Isn't that what I'm doing? I assume you mean something else, but if you have details of specifically what you're thinking about I'd appreciate it.

    With regards to the configuration of the cards, I know that one of them is in the top-most slot, and the other is about 4 slots further down or so.

    Do you know if there's a way for me to test my theory that Quicktime isn't using the hardware at all? Is there a diagnostic utility in OS X that will monitor GPU/CPU usage and give me a hint as to whether the graphics cards are actually maxed out or just sitting idle?

    Thanks again :).
  8. Shadow macrumors 68000


    Feb 17, 2006
    Keele, United Kingdom
    The x18, x8 ect refers to the speed of the slot the card is placed in. x16 is twice (theoretical) than x8, just as x8 is double the speed of x4, ect.
  9. Mackeyser macrumors member

    Jul 22, 2002
    Tampa, FL
    The PCI bus is configurable

    The PCI bus is configurable.

    The lowest slot (the double wide slot) is default configured for 16x. The rest can be configured in a number of ways where the other 3 slots have 10x available to them which means 1x, 1x, 8x or 1x, 4x, 4x...like that.

    What it means is that the primary graphics slot has 16 data lanes on the PCI bus whereas the topmost slot perhaps only has 1. Depends on how the PCI bus is configured. I haven't received my Mac Pro yet (late this week or early next) so I don't remember HOW to configure the bus, but it isn't hard, I DO remember that. I think there is even a thread on here about how to do it.

    Anyway, I presume the 7300GT is powering 2x24" each or 2x20" monitors, right? Because the 7300GT won't power 2x30" monitors. Only the x1900 and Quadro 4500 will power 2x30" each.

    Also, if you have 3 monitors in a grid, it could be struggling without the other display. I'd remove one of the monitors so that both monitors fully display the canvas and try it again. It could be that the odd monitor setup just isn't playing friendly with the drivers.

    Still, knowing the size of the monitors is important.
  10. Mackeyser macrumors member

    Jul 22, 2002
    Tampa, FL
    perfect, thanks.

    While I don't plan to have a second video card, I may get a Fiber Channel card later for an Xserve RAID as well as an AJA Kona card and I want to ensure they get as much bandwidth as they need without leaving any on the table, as it were.

    good lookin' out...
  11. Oreckel thread starter macrumors newbie

    Sep 18, 2006
    Aha, thanks. I'll take a look at that configuration screen and see if it seems obviously wrong. What is the maxium lanes the 7300GT can use (or how can I find out?). By the sound of it, the most efficient thing to do is use two 4x lane slots.

    Is there a way to find out if the specs on Radeon's website (I shared them in my first post) apply to a 1x, 4x, 8x, or 16x slot? I've never heard of any of this before.

    The monitors are two 24" LCD's (1920x1080 each), and the third is a 20" (1620x1050) (which actually means the desktop is 3840x2130 - just a bit taller since I was assuming the 2007FP was 1280x1024). I have a 19" that I can drag out and hook up as well if you think that's a problem, though I wouldn't think that would be the problem.

    Thanks again :).
  12. Mackeyser macrumors member

    Jul 22, 2002
    Tampa, FL
    Well, for one

    I would standardize the resolutions so that each monitor had the same res. It won't look the same, but it could be that the computer is trying to scale for each monitor in real time and THAT would be a HUGE processor task.

    Try standardizing the resolutions.

    As far as the PCI, someone already posted the Apple KB doc so that you can manually configure the bus.

    You should apply 16x to your primary card and 8x to the secondary card and it doesn't matter which slot, it looks like.
  13. FF_productions macrumors 68030


    Apr 16, 2005
    Mt. Prospect, Illinois
    Post some pics!
  14. Oreckel thread starter macrumors newbie

    Sep 18, 2006
    Here you go. Sorry the first one's out of focus - my battery was dying and I was in a rush to get the shots:


    I won't actually be able to get back and experiment with this for at least a week or so (since I'm heading off on vacation). But I've got this topic bookmarked and if/when I succed (or fail ;)) I'll post back after I get more information.

    Thanks again for all the help :).

Share This Page