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1080p not playing smoothly on 2.8GHz iMac

O

ozthegweat

macrumors regular
Original poster
Feb 20, 2007
247
229
Switzerland
I received my brandnew 2.8GHz iMac with a NVIDIA 8800 graphics card and 4GB RAM.

Very speedy, but one thing bugs me: the 1080p trailers from the Apple website don't always play smoothly. There are some moments where the framerate drops down, which I think shouldn't happen on such a powerful machine.

I also noticed it when watching 720p TV rips (.mkv files from Bittorrent) in QuickTime, which played smoothly in VLC though.

There are no other programs running, Spotlight isn't indexing, and it's reproducable.

One example I just tried: "Journey To The Center Of The Earth" trailer 4 in 1080p. At various times there is a noticeable drop in framerate. I saved the trailer to the hard disk and played it with VLC –*no problem.

What is the problem here? Why can't QuickTime handle it?
 
ozthegweat said:
I received my brandnew 2.8GHz iMac with a NVIDIA 8800 graphics card and 4GB RAM. Very speedy, but one thing bugs me: the 1080p trailers from the Apple website don't always play smoothly. There are some moments where the framerate drops down, which I think shouldn't happen on such a powerful machine. What is the problem here? Why can't QuickTime handle it?
Click to expand...

Quicktime's not very good. The best app for HD video playback is XBMC.
 
ozthegweat said:
At various times there is a noticeable drop in framerate. I saved the trailer to the hard disk and played it with VLC –*no problem. What is the problem here? Why can't QuickTime handle it?
Click to expand...

I know next-to-nothing about the technical aspects of iMac's video performance, but watching a DVD movie (on a new 3.06ghz 24" iMac), I was aware of what I'd call subtle disjointed movement in backgrounds (for example, when the camera was panning) or some fast-moving action scenes. I tried turning off the de-interlacing in the pull-down menu and I saw an improvement. No idea if that relates to what you are referring to, but thought I'd mention it.
 
Internet connection?

Maybe your internet connection can't keep up with it? If it works after you save it to disk then play back it would seem to be an internet connection issue.
 
Sir Cecil said:
I know next-to-nothing about the technical aspects of iMac's video performance, but watching a DVD movie (on a new 3.06ghz 24" iMac), I was aware of what I'd call subtle disjointed movement in backgrounds (for example, when the camera was panning) or some fast-moving action scenes. I tried turning off the de-interlacing in the pull-down menu and I saw an improvement. No idea if that relates to what you are referring to, but thought I'd mention it.
Click to expand...


Is this possibly also due to an inherent 'slow' response time of the LCD screen? The iMacs aren't as fast as the standard 'gaming' monitors, are they? Does anyone know the actual reponse time?

Morton
 
No, it has nothing to do with my internet connection. I waited for the movie to finish loading. I also played it back in QuickTime after saving it do disk. It also has nothing to do with the LCD, as the trailer plays perfectly in VLC.

I just looked at the system requirements for 1080p playback (from the Apple website):

QuickTime 7 for Mac OS X:
Dual 2.0 GHz PowerMac G5 or faster Macintosh computer; 2.0 GHz Intel Core Duo or faster
At least 512MB of RAM
128MB or greater video card

Has no one of you noticed anything like that? I restored a Time Machine backup from my MacBook Air, could that be the problem (even though I wouln't know why).
 
i also noticed general unsmooth video playback.
hd AND standard xvid,divx movies.
whenever theres a fast pan, the imac isnt as perceptively
smooth as e.g. my windows pentium4.
also, games running at <60 fps seem unsmooth IMHO.
maybe its the sheer screen estate and just a psychovisual imagination :)
 
XMBC is a pile of pooo!

Stick to VLC.

XMBC will not even go to full screen. & frustrating to use. Binning NOW!

PS Send the iMac back & get a refund! ;)
 
software update? not sure.
my white 24" iMac which is not as fast as yours plays 1080 p perfectly.
 
i wonder if the fact that HD video is 24 Hz and LCD screen is 60 Hz has anything to do with choppy video. I would think aliasing would come into play as it would have to play each frame 2.5 times, or 2 and 3 alternately. But i guess the source material is the most important aspect to the smoothness of the playback. Sounds like that new iMac might have to be returned.
 
i watched a bunch of hd trailers last night on a new 2.8 8800gs.. no noticeable lag except of course when it was still downloading
 
With white iMac 2.06 C2D, I have played 2 (or was it 3) 1080p trailers from Apple web site (saved on HD) at the same time with no loss in frame rate nor stuttering.

The white iMac is over 1 year old and can handle multiple 1080p files, thus a current iMac should be able to handle one 1080 file.

To Noobs, current and recent desktop LCDs, except the really cheap ones (which Apple does not use), can all handle video playback.
 
darrellishere said:
Stick to VLC.

XMBC will not even go to full screen. & frustrating to use. Binning NOW!

PS Send the iMac back & get a refund! ;)
Click to expand...

XBMC most certainly does do full screen. The problem here is not the program but the operator. It's not that hard to use either. ;)

Nothing plays HD content as smoothly as XBMC on a Mac. VLC, otoh, chokes on almost all 1080P I throw at it and even some 720P.

Cave Man said:
XBMC is known for its decoding abilities, not for it's pretty GUI. If we could get QT's GUI on XBMC's decoding algorithm, all would be good.
Click to expand...

I love the XBMC GUI. I far prefer it to Front Row which I have now effectively replaced with XBMC.

XBMC will only continue to improve.
 
SaSaSushi said:
XBMC most certainly does do full screen. The problem here is not the program but the operator. It's not that hard to use either. ;)

Nothing plays HD content as smoothly as XBMC on a Mac. VLC, otoh, chokes on almost all 1080P I throw at it and even some 720P.



I love the XBMC GUI. I far prefer it to Front Row which I have now effectively replaced with XBMC.

XBMC will only continue to improve.
Click to expand...

Video playback is good on the XMBC, it plays 1080p well that QT and VLC cannot. However there are several audio issues I've so far encountered with it, not forgetting some video playback issues with mkv files as well.

Most of the mkv (720p) files with AC3 audio I played do not have audio in XMBC, only except a tiny few. Most of the mkv movies are also played in accelerated motion, not sure why. I sure hope get some pointers over here.

Right now I'm avoiding 1080p movies because VLC and QT are not the best media for doing so, and as for XMBC only when it can support more audio playback and reaches 1.0.

For now I'll stick to 720p and QT as it plays them quite well.

If anyone has any advice for my XMBC playback issues, please kindly let me know! :)
 
Do you have Perian installed?

I had that problem too. 1080 movie trailers played fine in VLC but were occasionally (but always at the same places) dropping frames in QT. I kept the trailer for "Atonement" to check and the first stuttering occurs a few seconds into it even before any character speaks.

In the end, I discovered it was Perian which was responsible for the problem. Removing Perian made the problem go away.
 
orpheus1120 said:
Video playback is good on the XMBC, it plays 1080p well that QT and VLC cannot. However there are several audio issues I've so far encountered with it, not forgetting some video playback issues with mkv files as well.

Most of the mkv (720p) files with AC3 audio I played do not have audio in XMBC, only except a tiny few. Most of the mkv movies are also played in accelerated motion, not sure why. I sure hope get some pointers over here.
Click to expand...

I'm not sure exactly what's going on there but I can tell you I have yet to find the file that doesn't play audio perfectly with XBMC. I have a lot with AC3. I use the toslink out to a home theater if that makes a difference. Are you using the internal iMac speakers? I guess it would since XBMC isn't really playing anything but just streaming the data to the amp which decodes it.

XBMC is now my default media player. In library mode it blows Front Row out of the water.
 
Hello SaSaSushi, thanks for replying.

I'm playing through JBL Spot 2.1 speakers and sub from the imac.

Yes you are right. I had made a mistake earlier, AC3 audio does indeed play well in XBMC. The ones I'm having problem with are AAC audio that are Nero 6ch origins (as gathered from Motive Properties option in QT). The videos are in h.264 but somehow they would play in accelerated mode (seems like 2x) and there will not be audio.

I understand that XBMC only support a limited audio codecs (AAC being one of them). However I don't understand why it won't play the Nero's AAC then?
 
orpheus1120 said:
Yes you are right. I had made a mistake earlier, AC3 audio does indeed play well in XBMC. The ones I'm having problem with are AAC audio that are Nero 6ch origins (as gathered from Motive Properties option in QT). The videos are in h.264 but somehow they would play in accelerated mode (seems like 2x) and there will not be audio.

I understand that XBMC only support a limited audio codecs (AAC being one of them). However I don't understand why it won't play the Nero's AAC then?
Click to expand...

Hi, have you tried XBMC's forums? I could only find this post in a quick search and I'm not sure if it is applicable to your situation but I think it might be worth a look over there. :)
 
SaSaSushi, I think I know why I'm getting no audio from the mkv files I'm viewing. That's because currently version 0.5b2 does not support AAC 6 ch audio, that's why I'm not getting any sound. That alone should also be the reason why the movies are playing at accelerated motion.

AAC 6 ch support will be provided in ver. 0.6 which is supposed to arrive on 1st June.

Take a look at the roadmap.
 
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