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1080p playback stutters - any ideas?

peterdevries

peterdevries

macrumors 68040
Original poster
Feb 22, 2008
3,146
1,135
Amsterdam, The Netherlands
I own a previous generation late 2009 Mac mini c2d 2.26 ghz with 2 mb ram. I use the latest non-beta version of XBMC and have my libraries on two external usb2.0 external drives. I use a mini display port to HDMI converter.

Playback of 1080p movies is flaky. Sound is perfect but it appears frames are missing and the video is choppy. Everything is fine when I set video output to 720p.

Can anyone help here? Do I need to upgrade my ram to 4 Gb? Or is the speed of my external drives the bottleneck here?

Thanks in advance.
 
flopticalcube said:
Have you tried playing a movie from the internal drive? Could be the encoding used in the movies as well. Generally these things are CPU bound but the 2.26 C2D should be sufficient. Having said that, the USB interface does burden the CPU.
Click to expand...

I will try that. I would like to keep the movies on the external drive though, as I assumed the USB connection should be fast enough for 1080p playback. I just bought an extra 2tb disk for storage.

So the 2 Gb ram is not the problem?

Edit: I was lazy and never noticed that the ext. drive has FW800. I will connect it that way first to see if that makes a difference.
 
Last edited:
peterdevries said:
I will try that. I would like to keep the movies on the external drive though, as I assumed the USB connection should be fast enough for 1080p playback. I just bought an extra 2tb disk for storage.
Click to expand...

USB is enough but it uses CPU to transfer data (=less CPU for decoding)

So the 2 Gb ram is not the problem?
Click to expand...

Nope.

How high quality videos do you have? If they are very high quality Blu-Ray rips, then it's not a surprise that you're experiencing lags. One reason for that is audio decoding which is VERY CPU intensive.
 
peterdevries said:
I will try that. I would like to keep the movies on the external drive though, as I assumed the USB connection should be fast enough for 1080p playback. I just bought an extra 2tb disk for storage.

So the 2 Gb ram is not the problem?
Click to expand...

Shouldn't be as long as you are not doing anything else at the same time. I played 1080p from my 1.66 2GB mini that handled most 1080p.
 
Hellhammer said:
USB is enough but it uses CPU to transfer data (=less CPU for decoding)



Nope.

How high quality videos do you have? If they are very high quality Blu-Ray rips, then it's not a surprise that you're experiencing lags. One reason for that is audio decoding which is VERY CPU intensive.
Click to expand...

Hmmm. That would be crap, because I can't do anything about my processor speed.

I could use handbrake to re encode the files then from 5.1 to 2.1, as I don't use a surround system. That should at least help, right? Does any of you know whether re encoding the sound through handbrake also degrades or changes the video quality?

Thank you all for your insight by the way!
 
Last edited:
One very important, yet unanswered, question has already been asked.
What quality (bitrate, format) do the videos have?
1080p is not always 1080p. You can have a 5Mbit/s 1080p file and a 30Mbit/s 1080p file.

The other question is which software you are using for playback.


Personally, I use the exact same machine as you do (except for an internal SSD and my media is streamed over the network) and the machine handles all my files just fine.
My movies and tv-shows are .mkv files which I create using makeMKV (uncompressed but due to the MKV format without HD sound) and since uncompressed files are quite large (30 to 40GB) I generally put them through handbrake and make them smaller (reducing their bitrate, deleting subtitles and unrequired audio tracks). The differences in picture quality are completely negligible. Even if I put both files side by side on my screen, the differences are almost not visible.

Software wise, I use Plex. It supports hardware encoding for x264 encoded files (which my rips are), which is why I don't experience any dropped frames or stuttering. CPU usage is generally in the upper 80s whilst playback.
 
Can anyone tell me how I can find the bitrate for an MKV file? The VLC file inspector shows me all zeros.

I ripped the movies using the constant quality setting at the default percentage (I think 66%).

The software I use for playing the files is XBMC.
 
Maybe this calculator will help you.

Or you could just try encoding a film with HandBrake and use e.g. 15Mb/s (15000Kbps) as bitrate
 
Cave Man said:
It will bring up codec information, including bitrates.
Click to expand...

Thanks! It was actually the 'o' key though ;)... I made a screenshot. It shows a lot of dropped frames. Processor utilization is only about 30%, with a video bitrate of about 9,5 Mb/s.



It all doesn't sound too outrageous to me, or is that bitrate really high? The dropped frames go up when a lot of panning or moving is going on on screen. I connected the drive which holds the media with firewire800 t replace the USB2.0.

Any ideas? Thanks!
 
peterdevries said:
Thanks! It was actually the 'o' key though ;)... I made a screenshot. It shows a lot of dropped frames. Processor utilization is only about 30%, with a video bitrate of about 9,5 Mb/s.



It all doesn't sound too outrageous to me, or is that bitrate really high? The dropped frames go up when a lot of panning or moving is going on on screen. I connected the drive which holds the media with firewire800 t replace the USB2.0.

Any ideas? Thanks!
Click to expand...

That bitrate is pretty low, a good BR rip can be up to 50Mb/s. Can you see the CPU usage from another app (Activity Monitor) to confirm that it's only 30%?
 
peterdevries said:
Thanks! It was actually the 'o' key though ;)...
Click to expand...

Yeah, I don't use XBMC but instead Plex (a fork of XBMC). In Plex it's the 'I' key.

I made a screenshot. It shows a lot of dropped frames. Processor utilization is only about 30%, with a video bitrate of about 9,5 Mb/s.
Click to expand...

Something else is going on. That bit rate with AC3 isn't very high. Have you tried MPlayer OS X Extended or Plex for playback?
 
peterdevries said:
I own a previous generation late 2009 Mac mini c2d 2.26 ghz with 2 mb ram. I use the latest non-beta version of XBMC and have my libraries on two external usb2.0 external drives. I use a mini display port to HDMI converter.

Playback of 1080p movies is flaky. Sound is perfect but it appears frames are missing and the video is choppy. Everything is fine when I set video output to 720p.

Can anyone help here? Do I need to upgrade my ram to 4 Gb? Or is the speed of my external drives the bottleneck here?

Thanks in advance.
Click to expand...

Geez. Why are you not using the beta???????:confused::confused::confused::confused::confused:

http://mirrors.xbmc.org/releases/osx/xbmc-r35068-Dharma_beta4-x86.dmg

Use it.
 
dr. shdw said:
Geez. Why are you not using the beta???????:confused::confused::confused::confused::confused:

http://mirrors.xbmc.org/releases/osx/xbmc-r35068-Dharma_beta4-x86.dmg

Use it.
Click to expand...

The screenshot from somewhere above is actually from Dharma 4. I have been fiddling with a lot of settings since I read a few posts on the XBMC forum about hardware acceleration. In both versions of XBMC that I tried, performance improved markedly when I switched hardware acceleration OFF.

This increased CPU usage but made the video smoother. It is still not optimal though.
 
peterdevries said:
The screenshot from somewhere above is actually from Dharma 4. I have been fiddling with a lot of settings since I read a few posts on the XBMC forum about hardware acceleration. In both versions of XBMC that I tried, performance improved markedly when I switched hardware acceleration OFF.

This increased CPU usage but made the video smoother. It is still not optimal though.
Click to expand...

Hmm what OS version are you running? 10.6.5? Possibly try other ones, such as 10.6.3 since there maybe a HA bug somewhere.
 
i have exactly the same issue with many 1080p movies.
i was planing to increase the ram. but it seems from the responses above the ram has nothing to do with the issue!
 
OK, I have tried a number of different software (Plex, XBMC, VLC) and tweaks (re-encoding to lower bandwith, audio downix, all permutations of settings in XBMC :)) but am stuck with the stuttering at 1080p.

I have set output back to 720p and it is all good, except that the 1080p encoded video is still stuttering. Less, but still. 720p encoded video on 1080p also stutters..

So, i'm starting to think it's not settings or the video, but my hardware that is not up to the challenge. I have tried lots of things and lots of different video and always with the same result.

An example: at the beginning of Avatar, Jake get's pulled out of his hibernation chamber or whatever. There is a lot of stuff going on in that screen with a lot of movement, and the video stutters massively.

So. I'm thinking the following: would a ram upgrade help here (I know in this thread before it was stated that it was not the problem)? I own the late 2009 Mac Mini that has shared video ram. Would the ram upgrade also automatically increase the allocated video ram? Or is this set to maximally 256 Mb?

Thanks for amy pointers. I have a top of the line TV and would really like to watch 1080p content on it with my not-THAT-old Mac Mini.

Thanks again..
 
peterdevries said:
An example: at the beginning of Avatar, Jake get's pulled out of his hibernation chamber or whatever. There is a lot of stuff going on in that screen with a lot of movement, and the video stutters massively.
Click to expand...
would you post the timing of the scene so i can test it with mine and give you the result?


peterdevries said:
So. I'm thinking the following: would a ram upgrade help here (I know in this thread before it was stated that it was not the problem)? I own the late 2009 Mac Mini that has shared video ram. Would the ram upgrade also automatically increase the allocated video ram? Or is this set to maximally 256 Mb?
Click to expand...

if its 2009 model i can tell you from my experience:
1 GB get you 128 VRAM
2GB Ram get you 256 VRAM
4GB Ram get you 256 VRAM o
8GB Ram get you ??? VRAM <---haven't tried it maybe someone can let us know

but from what i read 256 is the maximum.

do we really need more than 256? read this
http://www.barefeats.com/mbpp22.html
 
64 mb of vRAM is plenty for 1080p video. The issue is one of playback, either hardware, software or codec. I suspect the latter, but without the OP's file it's tough to say with certainty. My 2 ghz GMA950 Mini plays most Blu-ray video without a hitch using Plex.

256 mb is the limit for the 9400 gpu under OS X. I have its fraternal twin in my hackintosh (9300) and if I set it to 512 mb of vRAM is stalls OS X something fierce. Return it to 256 and it works just fine.
 
Cave Man said:
64 mb of vRAM is plenty for 1080p video. The issue is one of playback, either hardware, software or codec. I suspect the latter, but without the OP's file it's tough to say with certainty. My 2 ghz GMA950 Mini plays most Blu-ray video without a hitch using Plex.

256 mb is the limit for the 9400 gpu under OS X. I have its fraternal twin in my hackintosh (9300) and if I set it to 512 mb of vRAM is stalls OS X something fierce. Return it to 256 and it works just fine.
Click to expand...

I suspected something like that. I also wasn´t really motivated to upgrade my ram, as it´s difficult or expensive.

I heard that there is a perfectly encoded file doing the rounds, which is a snippet form the BBC Earth BluRay disks. Apparently this file is something like the benchmark for encoding. Does anyone have a link to this file? I could use it to determine whether it´s the encoding of the files or the hardware that´s the problem.
 
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